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" '''WH 




A Skiagraph. 



THE 
STORY OF ELECTRICITY 



BY 



JOHN MUNRO 



AUTHOR OF ELECTRICITY AND ITS USES, PIONEERS OF ELECTRICITY, 

HEROES OF THE TELEGRAPH, ETC., AND JOINT AUTHOR OF 

MUNRO AND JAMIESON's POCKET-BOOK OF 

ELECTRICAL RULES AND TABLES 



WITH ONE HUNDRED ILLUSTRATIONS 



3 '•, ^5-' 5 D 53 5 "D-" 



NEW YORK 

D. APPLETON AND COMPANY 

1902 



THF t»BRA«Y OF 
CONGRESS. 

T^) C4*nr^ RtOfctWCD 

NOV, 2^ 1902 

Cn^vmoMT fKfwv 
C ft*8*-^'irx« Ho. 



C<1PYKIGHT, 1896, 1902, 

By D. APPLETON AND COMPANY. 



PUBLISHERS' NOTE. 



For our edition of this work the terminolo- 
gy has been altered to conform with American 
usage, some new matter has been added, and a 
few of the cuts have been changed and some 
new ones introduced, in order to adapt the book 
fully to the practical requirements of American 
readers. 



CONTENTS. 



CHAPTER 

I. The Electricity of Friction 
II. The Electricity of Chemistry 

III. The Electricity of Heat 

IV. The Electricity of Magnetism 
V. Electrolysis .... 

VI. The Telegraph and Telephone 
VII. Electric Light and Heat 
VIII. Electric Power 
IX. Minor Uses of Electricity . 
X. The Wireless Telegraph 
List of Books .... 
Appendix ..... 
Index 



PAGE 

9 
26 

41 

45 

74 

81 

no 

124 

143 

174 
179 
181 
189 



I 



LIST OF ILLUSTRATIONS. 



FIGURE 


PAGE 


FIGURE PAGE 


A Skiagraph Frontisp 


iece 


24 — A Thermo - electric 




I — A Frictional Ma- 




Pile 


44 


chine 


II 


25 — A Natural Magnet , 


48 


2 . . . . • 


12 


26 


50 


3 


13 


27 


53 


4 


14 


28 . . . 


54 


5 . • . 


17 


29 . . 


55 


6 


18 


30 — The Galvanoscope . 


56 


7 


19 


31 


57 


8 — The Electrophorus . 


20 


32 


58 


9 — The Leyden Jar 


22 


33 


59 


lo — A Wimshurst Ma- 




34 


60 


chine . 


24 


35 


61 


II— A Voltaic Cell . 


28 


36 — The Induction Coil . 


63 


12 . 


29 


37 


64 


13 — Cells in Series . 


30 


38 


65 


14— Cells in Parallel 


30 


39 


66 


15— A Daniell Cell . 


33 


40— A Dynamo 


68 


16 — The Leclanche Cell 


34 


41 


70 


17— The Bichromate Cell 


i 35 


42 


71 


18— The Chloride of Sil- 




43 


72 


verCell. 


35 


44 . ' . 


78 


19— TheE.C. C. DryCel 


I 37 


45 


84 


20 — The Voltameter 


38 


46 — Morse Signal Alpha- 




21— The E. P. S. Accu- 




bet . . . 


87 


mulator 


40 


47 — A Simple Electro 




22 — A Thermo - electric 




Magnet . 


88 


Couple . 


. 41 


48 — Electro Magnet 


89 


23 — Thermo-electric Cou- 




49 — The Morse Instru- 




ples in Series 


. 43 


ment 


89 



LIST OF ILLUSTRATIONS. 



FIGU 


RE 


PAGE 


FIGURE 


PAGE 1 


50- 


-The Sounder . 


90 


75 ... . 


124 1 


51- 


-Sections of the 1894 




76 ... . 


125 




Atlantic Cable — 




77 — An Electric Railway 


127 




Actual Sizes — 




78 — An Electric Carriage 


129 




Irish Shore End 


96 


79 — An Electric Launch 


130 




Newfoundland 




80— An Electric Fan 


131 




Shore End . 


97 


81 — An Electric Sewing 






Deep Sea . 


97 


Machine 


132 




Light Interme- 




82— An Electric Drill 


133 




diate 


97 


83 — An Electric Trem- 






Heavy Interme- 




bling Bell . 


143 




diate 


97 


84 . . . 


144 


52- 


-The Mirror Instru- 




85 . . . . 


. 145 




ment 


98 


86 . 


146 


53 


. 


99 


87 — A Magneto-Electric 




54- 


-The Siphon Recorder 


100 


Bell . 


. 147 


55 


. 


lOI 


88 . 


148 


56- 


-The Telephone 


102 


89— The Electric "But- 




57- 


-The Microphone 


104 


terfly " Clock 


. 151 


58 


. 


106 


90 . 


152 


59 




108 


91 — The Photophone 


. 153 


60 




III 


92— The Induction Bal- 




61- 


-The Pilsen Lamp 


112 


ance . 


155 


62- 


-The Brush Lamp 


113 


93— The Electric Pen 


156 


63- 


-The Edison Lamp . 


115 


94 — The Phonograph 


159 


64 




116 


95 — An Electric Gas 




65 




116 


Lighter 


. 160 


66 




118 


96 — An Electric Lamp 




67 




118 


Lighter 


. 162 


68 




119 


97 — An Electric Fuse 


163 


69- 


-Electrical Phospho- 




98 . . . . 


. 164 




rescence 


120 


99 . . . . 


165 


70- 


-The Ideal lUumi- 




100 — Photographing the 






nant 


121 


Unseen 


171 


71 




122 


loi — Photographing the 




72 




123 


Skeleton 


172 


73 


, 


123 


102 — Marconi's Appara 




74 


.00,. 


123 


tus 


. 177 



THE STORY OF ELECTRICITY. 



CHAPTER I. 

THE ELECTRICITY OF FRICTION. 

A SCHOOLBOY who rubs a stick of sealing-wax 
on the sleeve of his jacket, then holds it over 
dusty shreds or bits of straw to see them fly up 
and cling to the wax, repeats without knowing 
it the fundamental experiment of electricity. In 
rubbing the wax on his coat he has electrified it, 
and the dry dust or bits of wool are attracted to it 
by reason of a mysterious process which is called 
** induction." 

Electricity, like fire, was probably discovered 
by some primeval savage. According to Hum- 
boldt, the Indians of the Orinoco sometimes 
amuse themselves by rubbing certain beans to 
make them attract wisps of the wild cotton, and 
the custom is doubtless very old. Certainly the 
ancient Greeks knew that a piece of amber had 
when rubbed the property of attracting light 
bodies. Thales of Miletus, wisest of the Seven 
Sages, and father of Greek philosophy, explained 
this curious effect by the presence of a "soul " in 
the amber, whatever he meant by that. Thales 
flourished 600 years before the Christian era, 
while Croesus reigned in Lydia, and Cyrus the 
Great, in Persia, when the renowned Solon gave 

9 



lO THE STORY OF ELECTRICITY. 

his laws to Athens, and Necos, King of Egypt, 
made war on Josiah, King of Judah, and after de- 
feating him at Megiddo, dedicated the corslet he 
had worn during the battle to Apollo Didymaeus 
in the temple of Branchidae, near Miletus. 

Amber, the fossil resin of a pine tree, was 
found in Sicily, the shores of the Baltic, and 
other parts of Europe. It was a precious stone 
then as now, and an article of trade with the 
Phoenicians, those early merchants of the Medi- 
terranean. The attractive power might enhance 
the value of the gem in the eyes of the supersti- 
tious ancients, but they do not seem to have in- 
vestigated it, and beyond the speculation of 
Thales, they have told us nothing more about it. 

Towards the end of the sixteenth century Dr. 
Gilbert of Colchester, physician to Queen Eliza- 
beth, made this property the subject of experi- 
ment, and showed that, far from being peculiar 
to amber, it was possessed by sulphur, wax, glass, 
and many other bodies which he called electrics^ 
from the Greek word elekiron, signifying amber. 
This great discovery was the starting-point of the 
modern science of electricity. That feeble and 
mysterious force which had been the wonder of 
the simple and the amusement of the vain could 
not be slighted any longer as a curious freak of 
nature, but assuredly none dreamt that a day was 
dawning in which it would transform the world. 

Otto von Guericke, burgomaster of Magde- 
burg, was the first to invent a machine for excit- 
ing the electric power in larger quantities by 
simply turning a ball of sulphur between the bare 
hands. Improved by Sir Isaac Newton and others, 
who employed glass rubbed with silk, it created 
sparks several inches long. The ordinary fric- 



THE ELECTRICITY OF FRICTION. 



II 



tional machine as now made is illustrated in fig- 
ure I, where /^ is a disc of plate glass mounted 
on a spindle and turned by hand. Rubbers of 




Fig. I.— a Frictional Machine. 

silk R, smeared with an amalgam of mercury and 
tin, to increase their efficiency, press the rim of 
the plate between them as it revolves, and a brass 
conductor C, insulated on glass posts, is fitted 
with points like the teeth of a comb, which, as the 
electrified surface of the plate passes by, collect 
the electricity and charge the conductor with posi- 
tive electricity. Machines of this sort have been 
made with plates 7 feet in diameter, and yielding 
sparks nearly 2 feet long. 

The properties of the " electric fire," as it was 
now called, were chiefly investigated by Dufay. 
To refine on the primitive experiment let us re- 
place the shreds by a pithball hung from a sup- 
port by a silk thread, as in figure 2. If we rub 
the glass rod vigorously with a silk handkerchief 
and hold it near, the ball will fly toward the rod. 



12 THE STORY OF ELECTRICITY. 

Similarly we may rub a stick of sealing wax, a 
bar of sulphur, indeed, a great variety of sub- 
stances, and by this easy test we shall find them 
electrified. Glass rubbed with glass will not show 
any sign of electrification, nor will wax rubbed on 
wax ; but when the rubber is of a different mate- 
rial to the thing rubbed, we shall find, on using 
proper precautions, that electrici- 
ty is developed. In fact, the 
property which was once thought 
peculiar to amber is found to be- 
long to all bodies. Any substance^ 
when rubbed with a different sub- 
stance^ beco7nes electrified. 

The electricity thus 
produced is termed fric- 
tional electricity. Of 
course there are some 
materials, such as am- 
ber, glass, and wax, 
which display the ef- 
fect much better than 
Fig. 2. ^^ others, and hence its 

original discovery. 
In dry frosty weather the friction of a tortoise- 
shell comb will electrify the hair and make it cling 
to the teeth. Sometimes persons emit sparks in 
pulling off their flannels or silk stockings. The 
fur of a cat, or even of a garment, stroked in the 
dark with a warm dry hand will be seen to glow, 
and perhaps heard to crackle. During winter a 
person can electrify himself by shuffling in his 
slippers over the carpet, and light the gas with a 
spark from his finger. Glass and sealing-wax are, 
however, the most convenient means for investi- 
gating the electricity of friction. 




THE ELECTRICITY OF FRICTION. 



13 




A glass rod when rubbed with a silk handker- 
chief becomes, as we have seen, highly electric, 
and will attract a pithball (fig. 2). 
Moreover, if we substitute the 
handkerchief for the rod it will 
also attract the ball (fig. 3). Clear- 
ly, then, the handkerchief which 
rubbed the rod as 
well as the rod it- 
self is electrified. At 
first we might sup- 
pose that the hand- 
kerchief had merely 
rubbed off some of 
the electricity from the rod, but a lit- 
tle investigation will soon show that 
is not the case. If we allow the pith- 
ball to touch the glass rod it will steal some of 
the electricity on the rod, and we shall now find 
the ball i-epelled by the rod, as illustrated in figure 
4. Then, if we withdraw the rod and bring for- 
ward the handkerchief, we shall find the ball at- 
tracted by it. Evidently, therefore, the electricity 
of the handkerchief is of a different kind from 
that of the rod. 

Again, if we allow the ball to touch the hand- 
kerchief and rub off some of its electricity, the 
ball will be repelled by the handkerchief and at- 
tracted by the rod. Thus we arrive at the con- 
clusion that whereas the glass rod is charged with 
one kind of electricity, the handkerchief which 
rubbed it is charged with another kind, and, judg- 
ing by their contrary effects on the charged ball 
or indicator, they are of opposite kinds. To dis- 
tinguish the two sorts, one is called positive and 
the other negative electricity. 




14 THE STORY OF ELECTRICITY. 

Further experiments with other substances 
will show that sometimes the rod is negative 
while the rubber is positive. Thus, if 
we rub the glass rod with cat's fur 
instead of silk, we shall find the glass 
negative and the fur positive. Again, 
if we rub a stick of sealing-wax with 
the silk handkerchief, we shall find 
the wax negative and the silk 
positive. But in every case one 
is the opposite of the other, and 
moreover, an equal quanti- 
ty of both sorts of electrici- 
ty is developed, one kind on 
the rod and the other on the 
rubber. Hence we conclude 
that equal and opposite quan- 
^^' ^* titles of electricity are sim- 

ultaneously developed by friction. 

If any two of the following materials be 
rubbed together, that higher in the list becomes 
positively and the other negatively electrified: — 

Positive ( + ). 
Cats' fur. 
Polished glass. 
Wool. 

Cork, at ordinary temperature. 
Coarse brown paper. 
Cork, heated. 
White silk. 
Black silk. 
Shellac. 
Rough glass. 

Negative (— ). 



THE ELECTRICITY OF FRICTION. 15 

The list shows that quality, as well as kind, 
of material affects the production of electricity. 
Thus polished glass when rubbed with silk is 
positive, whereas rough glass is negative. Cork 
at ordinary temperature is positive when rubbed 
with hot cork. Black silk is negative to white 
silk, and it has been observed that the best radi- 
ator and absorber of light and heat is the most 
negative. Black cloth, for instance, is a better 
radiator than white, hence in the Arctic regions, 
where the body is much warmer than the sur- 
rounding air, many wild animals get a white coat 
in winter, and in the tropics, where the sunshine 
is hotter than the body, the European dons a 
white suit. 

The experiments of figures i, 2, and 3 have 
also shown us that w^hen the pithball is charged 
with the positive electricity of the glass rod it is 
repelled by the like charge upon the rod, and 
attracted by the negative or unlike charge on the 
handkerchief. Again, when it is charged with 
the negative electricity of the handkerchief it is 
repelled by the like charge on the handkerchief 
and attracted by the positive or unlike charge on 
the rod. Therefore it is usual to say that like 
electricities repel and unlike electricities attract each 
other. 

We have said that all bodies yield electricity 
under the friction of dissimilar bodies ; but this 
cannot be proved for every body by simply hold- 
ing it in one hand and rubbing it with the excitor, 
as may be done in the case of glass. For instance, 
if we take a brass rod in the hand and apply the 
rubber vigorously, it will fail to attract the pith- 
ball, for there is no trace of electricity upon it. 
This is because the metal differs from the glass 



1 6 THE STORY OF ELECTRICITY. 

in another electrical property, and they must 
therefore be differently treated. Brass, in fact, 
is a conductor of electricity and glass is not. In 
other words, electricity is conducted or led away 
by brass, so that, as soon as it is generated by the 
friction, it flows through the hand and body of 
the experimenter, which are also conductors, and 
is lost in the ground. Glass on the other hand, 
is an insulator, and the electricity remains on the 
surface of it. If, however, we attach a glass 
handle to the rod and hold it by that whilst rub- 
bing it, the electricity cannot then escape to the 
earth, and the brass rod will attract the pith-ball. 
All bodies are conductors of electricity in 
some degree, but they vary so enormously in 
this respect that it has been found convenient 
to divide them into two extreme classes — con- 
ductors and insulators. These run into each 
other through an intermediate group, which are 
neither good conductors nor good insulators. 
The following are the chief examples of these 
classes : — 

Conductors. — All the metals, carbon. 

Intermediate (bad conductors and bad in- 
sulators). — Water, aqueous solutions, moist 
bodies ; wood, cotton, hemp, and paper in 
any but a dry atmosphere ; liquid acids, 
rarefied gases. 

Insulators. — Paraffin (solid or liquid), ozo- 
kerit, turpentine, silk, resin, sealing-wax or 
shellac, indiarubber, gutta percha, ebonite, 
ivory, dry wood, dry glass or porcelain, 
mica, ice, air at ordinary pressures. 

It is remarkable that the best conductors of 
electricity, that is to say, the substances which 



THE ELECTRICITY OF FRICTION. 



17 




offer least resistance to its passage, for instance the 
metals, are also the best conductors of heat, and 
that insulators made red hot become conductors. 
Air is an excellent insulator, and hence we are 

able to perform 
'•^..^ our experiments 

""*•'.. on frictional elec- 
^, .'•'' I tricity in it. We 
-*'' 1 can also run bare 

' telegraph wires 
through it, \ by taking care to insulate 

them with glass or porcelain from the 

wooden poles which support them 

above the ground. Water, on the other 

hand, is a partial conductor, and a great 

enemy to the storage or conveyance of 

electricity, from its habit of soaking in- 

to porous metals, or depositing in a 

film of dew on the cold surfaces of insu- 

lators such as glass, porcelain, or ebon- 

ite. The . remedy is to exclude it, or 

keep the ^ insulators warm and dry, or 

coat them ' ^' with shellac varnish, wax, or 

paraffin. Submarine telegraph wires running un- 
der the sea are usually insulated from the sur- 
rounding water by india-rubber or gutta percha. 

The distinction between conductors and non- 
conductors or insulators was first observed by 
Stephen Gray, a pensioner of the Charter-house. 
Gray actually transmitted a charge of electricity 
along a pack-thread insulated with silk, to a dis- 
tance of several hundred yards, and thus took 
an important step in the direction of the electric 
telegraph. 

It has since been found thsit fn'cfio/ia/ electrici- 
ty appears only on the external surface of conductors, 
2 



i8 



THE STORY OF ELECTRICITY. 



This is well shown by a device of Faraday 
resembling a small butterfly net insulated by a 
glass handle (fig. 5). If the net be charged it is 
found that the electrification is only outside, and 
if it be suddenly drawn outside in, as shown by 
the dotted line, the electrification is still found 
outside, proving that the charge has shifted from 
the inner to the outer surface. In the same way 
if a hollow conductor is charged with electricity, 
none is discoverable in the interior. Moreover, 
its distribution on the exterior is influenced by the 
shape of the outer surface. On a sphere or ball 
it is evenly distributed all round, but it accu- 
mulates on sharp edges or corners, and most of 
all on points, from which it is easily discharged. 

A neutral body can, as we have seen (fig. 4), 
be charged by contact with an electrified body ; 
but it can also be charged 
by induction, or the influence 
of the electrified body at a 
distance. 

Thus if we electrify a 
glass rod positively ( + ) and 
bring it near a neutral or 
unelectrified brass ball, in- 
sulated on a glass support, 
as in figure 6, we shall find 
the side of the ball next the 
rod no longer neutral but 
negatively electrified ( — ), 
and the side away from 
the rod positively elec- 
trified (-f). 
If we take away the rod again the ball will 
return to its neutral or non-electric state, show- 
ing that the charge was temporarily induced by 






Fig. 6. 



THE ELECTRICITY OF FRICTION. 



19 



the presence of the electrified rod. Again, if, as 
in figure 7, we have two insulated balls touching 
each other, and bring the rod up, that nearest 
the rod will become negative and that farthest 
from it positive. It appears from these facts 
that electricity has 
the power of disturb- 
ing or decomposing 
the neutral state of a 
neighbouring conduct- 
or, and attracting the 
unlike while it re- 
pels the like induced 
charge. Hence, too, 
it is that the electri- 
fied amber or sealing- 
wax is able to attract 
a light straw or pith- 
ball. The effect sup- 
plies a simple way of 
developing a large 
amount of electricity from a small initial charge. 
For if in figure 6 the positive side of the ball be 
connected for a moment to earth by a conductor, 
its positive charge will escape, leaving the nega- 
tive on the ball, and as there is no longer an 
equal positive charge to recombine w^ith it when 
the exciting rod is withdrawn, it remains as a 
negative charge on the ball. Similarly, if we 
separate the two balls in figure 7, we gain two 
equal charges — one positive, the other negative. 
These processes have only to be repeated by a 
machine in order to develop very strong charges 
from a feeble source. 

Faraday saw that the intervening air played a 
part in this action at a distance, and proved con- 




FlG. 7. 



20 



THE STORY OF ELECTRICITY. 



clusively that the value of the induction depended 
on the nature of the medium between the induced 
and the inducing charge. He showed, for exam- 
ple, that the induction through an intervening 
cake of sulphur is greater than through an equal 
thickness of air. This property of the medium is 
termed its inductive capacity. 

The Electrophorus, or carrier of electricity, is 
a simple device for developing and conveying a 
charge on the principle of induction. It consists, 




Fig. 8.— The Electrophorus. 

as shown in figure 8, of a metal plate B having 
an insulating handle of glass H, and a flat cake 
of resin or ebonite R. If the resin is laid on a 
table and briskly rubbed with cat's fur it becomes 
negatively electrified. The brass plate is then 
lifted by the handle and laid upon the cake. It 
touches the electrified surface at a few points, 
and takes a minute charge from these by contact. 



THE ELECTRICITY OF FRICTION. 2 1 

The rest of it, however, is insulated from the 
resin by the air. In the main, therefore, the 
negative charge of the resin is free to induce an 
opposite or positive charge on the lower surface 
and a negative charge on the upper surface of 
the plate. By touching this upper surface with 
the finger, as shown in figure 8, the negative 
charge will escape through the body to the 
ground or '' earth," as it is technically called, 
and the positive charge will remain on the plate. 
We can withdraw it by lifting the plate, and 
prove its existence by drawing a spark from it 
with the knuckle. The process can be repeated 
as long as the negative charge continues on the 
resin. 

These tiny sparks from the electrophorus, or 
the bigger discharges of an electrical machine, 
can be stored in a simple apparatus called a 
Leyden jar, which was discovered by accident. 
One day Cuneus, a pupil of Muschenbroeck, pro- 
fessor in the University of Leyden, was trying 
to charge some water in a glass bottle by con- 
necting it with a chain to the sparkling knob of 
an electrical machine. Holding the bottle in one 
hand, he undid the chain wnth the other, and 
received a violent shock which cast the bottle on 
the floor. Muschenbroeck, eager to verify the 
phenomenon, repeated the experiment, with a 
still more lively and convincing result. His 
nerves were shaken for two days, and he after- 
wards protested that he would not suffer another 
shock for the whole kingdom of France. 

The Leyden jar is illustrated in figure 9, and 
consists in general of a glass bottle partly coated 
inside and out with tinfoil F, and having a brass 
knob K connecting with its internal coat. When 



22 



THE STORY OF ELECTRICITY. 



the charged plate or conductor of the electro- 
phorus touches the knob the inner foil takes a 
positive charge, which induces a negative charge 




Fig. 9. — The Leyden Jar. 



in the outer foil through the glass. The corre- 
sponding positive charge induced at the same 
time escapes through the hand to the ground or 
"earth." The inner coating is now positively 
and the outer coating negatively electrified, and 
these two opposite charges bind or hold each 
other by mutual attraction. The bottle will 
therefore continue charged for a long time ; in 
short, until it is purposely discharged or the two 
electricities combine by leakage over the surface 
of the glass. 

To discharge the jar we need only connect the 
two foils by a conductor, and thus allow the 
separated charges to combine. This should be 
done by joining the outer to the inner coat with a 
stout wire, or, better still, the discharging tongs 
T, as shown in the figure. Otherwise, if the 



THE ELECTRICITY OF FRICTION. 23 

tongs are first applied to the inner coat, > the 
operator will receive the charge through his 
arms and chest in the manner of Cuneus and 
Muschenbroeck. 

Leyden jars can be connected together in 
*^ batteries," so as to give very powerful effects. 
One method is to join the inner coat of one to 
the outer coat of the next. This is known as 
connecting in *^ series," and gives a very long 
spark. Another method is to join the inner coat 
of one to the inner coat of the next, and similarly 
all the outer coats together. This is called con- 
necting ^^ in parallel," or quantity, and gives a 
big, but not a long spark. 

Of late years the principle of induction, which 
is the secret of the Leyden jar and electrophorus, 
has been applied in constructing " influence " 
machines for generating electricity. Perhaps the 
most effective of these is the Wimshurst, which 
we illustrate in figure 10, where PP are two 
circular glass plates which rotate in opposite 
directions on turning the handle. On the outer 
rim of each is cemented a row of radial slips of 
metal at equal intervals. The slips at opposite 
ends of a diameter are connected together twice 
during each revolution of the plates by wire 
brushes S, and collecting combs TT serve to 
charge the positive and negative conductors CC, 
which yield very powerful sparks at the knobs 
K above. The given theory of this machine may 
be open to question, but there can be no doubt 
of its wonderful performance. A small one pro- 
duces a violent spark 8 or 10 inches long after a 
few turns of the handle. 

The electricity of friction is so unmanageable 
that it has not been applied in practice to any 



24 



THE STORY OF ELECTRICITY. 



great extent. In 1753 Mr. Charles Morrison, of 
Greenock, published the first plan of an electric 
telegraph in the Scots Magazine^ and proposed to 
charge an insulated wire at the near end so as to 



K j^ 




Fig. 10. — A Wimshurst Machine. 



make it attract printed letters of the alphabet at 
the far end. Sir Francis Ronalds also invented a 
telegraph actuated by this kind of electricity, but 
neither of these came into use. Morrison, an 
obscure genius, was before his age, and Ronalds 
was politely informed by the Government of his 



THE ELECTRICITY OF FRICTION. 25 

day that " telegraphs of any kind were wholly 
unnecessary." Little instruments for lighting gas 
by means of the spark are, however, made, and 
the noxious fumes of chemical and lead works 
are condensed and laid by the discharge from the 
Wimshurst machine. The electricity shed in the 
air causes the dust and smoke to adhere by in- 
duction and settle in flakes upon the sides of 
the flues. Perhaps the old remark that '' smuts " 
or " blacks" falling to the ground on a sultry day 
are a sign of thunder is traceable to a similar 
action. 

The most important practical result of the 
early experiments with frictional electricity was 
Benjamin Franklin's great discovery of the iden- 
tity of lightning and the electric spark. One 
day in June, 1792, he went to the common at 
Philadelphia and flew a kite beneath a thunder- 
cloud, taking care to insulate his body from the 
cord. After a shower had wetted the string and 
made it a conductor, he was able to draw sparks 
from it with a key and to charge a Leyden jar. 
The man who had " robbed Jupiter of his thun- 
derbolts " became celebrated throughout the 
world, and lightning rods or conductors for the 
protection of life and property were soon brought 
out. These, in their simplest form, are tapes or 
stranded wires of iron or copper attached to the 
walls of the building. The lower end of the con- 
ductor is soldered to a copper plate buried in the 
moist subsoil, or, if the ground is rather dry, in a 
pit containing coke. Sometimes it is merely sol- 
dered to the water mains of the house. The 
upper end rises above the highest chimney, tur- 
ret, or spire of the edifice, and branches into 
points tipped with incorrosive metal, such as 



26 THE STORY OF ELECTRICITY. 

platinum. It is usual to connect all the outside 
metal of the house, such as the gutters and finials 
to the rod by means of soldered joints, so as to 
form one continuous metallic network or artery 
for the discharge. 

When a thundercloud charged with electricity 
passes over the ground, it induces a charge of an 
opposite kind upon it. The cloud and earth with 
air between are analogous to the charged foils of 
the Leyden jar separated by the glass. The two 
electricities of the jar, we know, attract each 
other, and if the insulating glass is too weak 
to hold them asunder, the spark will pierce it. 
Similarly, if the insulating air cannot resist the 
attraction between the thundercloud and the 
earth, it will be ruptured by a flash of lightning. 
The metal rod, however, tends to allow the two 
charges of the cloud and earth to combine quietly 
or to shunt the discharge past the house. 



CHAPTER II. 

THE ELECTRICITY OF CHEMISTRY. 

A MORE tractable kind of electricity than that 
of friction was discovered at the beginning of 
the present century. The story goes that some 
edible frogs were skinned to make a soup for 
Madame Galvani, wife of the professor of anatomy 
in the University of Bologna, who was in delicate 
health. As the frogs were lying in the laboratory 
of the professor they were observed to twitch 
each time a spark was drawn from an electrical 
machine that stood by. A similar twitching was 



THE ELECTRICITY OF CHEMISTRY. 27 

also noticed when the limbs were hung by copper 
skewers from an iron rail. Galvani thought the 
spasms were due to electricity in the animal, and 
produced them at will by touching the nerve of a 
limb with a rod of zinc, and the muscle with a 
rod of copper in contact with the zinc. It was 
proved, however, by Alessandra Volta, professor 
of physics in the University of Pavia, that the 
electricity w^as not in the animal, but generated 
by the contact of the two dissimilar metals and 
the moisture of the flesh. Going a step further, 
in the year 1800 he invented a new source of 
electricity on this principle, which is known as 
" Volta's pile." It consists of plates or discs of 
zinc and copper separated by a wafer of cloth 
moistened with acidulated water. When the zinc 
and copper are joined externally by a wire, a 
current of electricity is found in the wire. One 
pair of plates with the liquid between makes a 
'* couple " or element ; and two or more, built one 
above another in the same order of zinc, copper, 
zinc, copper, make the pile. The extreme zinc 
and copper plates, when joined by a wire, are 
found to deliver a current. 

This form of the voltaic, or, as it is sometimes 
called, galvanic battery, has given place to the 
"cell" show^n in figure 11, where the two plates 
Z C are immersed in acidulated water within the 
vessel, and connected outside by the wire W, 
The zinc plate has a positive and the copper a 
negative charge. The positive current flows from 
the zinc to the copper inside the cell and from the 
copper to the zinc outside the cell, as shown by 
the arrows. It thus makes a complete round, 
which is called the voltaic " circuit," and if the 
circuit is broken anywhere it will not flow at all. 



THE STORY OF ELECTRICITY. 




Fig. II. 
A Voltaic Cell. 



The positive electricity of the zinc appears to trav- 
erse the liquid to the copper, from which it flows 
through the wire to the zinc. 
The effect is that the end of the 
wire attached to the copper is 
positive ( + ), and called the 
positive '' pole " or electrode, 
while the end attached to the 
zinc is negative (— ), and called 
the negative pole or electrode. 
*' A simple and easy way to 
avoid confusion as to the direc- 
tion of the current, is to remem- 
ber that \.\\^ positive current flows 
ff'om the copper /^ the zinc at the 
point of metallic contact." 
The generation of this current is accompanied 
by chemical action in the cell. Experiment shows 
that the mere contact of dissimilar materials, such 
as copper and zinc, electrifies them — zinc being 
positive and copper negative ; but contact alone 
does not yield a continuous current of electricity. 
When we plunge the two metals, still in contact, 
either directly or through a wire, into water pref- 
erably acidulated, a chemical action is set up, the 
water is decomposed, and the zinc is consumed. 
Water, as is well known, consists of oxygen and 
hydrogen. The oxygen combines with the zinc 
to form oxide of zinc, and the hydrogen is set free 
as gas at the surface of the copper plate. So 
long as this process goes on, that is to say, as 
long as there is zinc and water left, we get an 
electric current in the circuit. The existence of 
such a current may be proved by a very simple 
experiment. Place a penny above and a dime be- 
low the tip of the tongue, then bring their edges 



THE ELECTRICITY OF CHEMISTRY. 



29 



into contact, and you will feel an acid taste in the 
mouth. 

Figure 12 illustrates the supposed chemical 
action in the ceil. On the left hand are the 



4^ 



00 



oooOcOoOcO 

00 
00 



00 

SBoooocoo 

00 
o 



FiG. 12. 

zinc and copper plates (Z C) disconnected in the 
liquid. The atoms of zinc are shown by small 
circles; the molecules of water, that is, oxygen, 
and hydrogen (ZTg O) by lozenges of unequal size. 
On the right hand the plates are connected by a 
wire outside the cell ; the current starts, and the 
chemical action begins. An atom of zinc unites 
with an atom of oxygen, leaving two atoms of 
hydrogen thus set free to combine with another 
atom of oxygen, which in turn frees two atoms of 
hydrogen. This interchange of atoms goes on 
until the two atoms of hydrogen which are freed 
last abide on the surface of the copper. The 
*' contact electricity " of the zinc and copper prob- 
ably begins the process, and the chemical action 
keeps it up. Oxygen, being an " electro-negative " 
element in chemistry, is attracted to the zinc, and 
hydrogen, being "electro-positive," is attracted 
to the copper. 

The difference of electrical condition or '^ po- 
tential " between the plates by which the current 
is started has been called the electrotnotive force, or 
force which puts the electricity in motion. The 



50 



THE STORY OF ELECTRICITY. 



obstruction or hindrance which the electricity 
overcomes in passing through its conductor is 
known as the resistance. Obviously the higher 
the electromotive force and the lower the resist- 
ance, the stronger will be the current in the con- 
ductor. Hence it is desirable to have a cell which 
will give a high electromotive force and a low in- 
ternal resistance. 

Voltaic cells are grouped together in the mode 
of Leyden jars. Figure 13 shows how they are 




Fig. 13. — Cells in Series. 

joined ^' in series," the zinc or negative pole of 
one being connected by wire to the copper or 
positive pole of the next. This arrangement mul- 




FiG. 14.— Cells in Parallel. 

tiplies alike the electromotive force and the re- 
sistance. The electromotive force of the battery 
is the sum of the electromotive forces of all the 



THE ELECTRICITY OF CHEMISTRY. 3 1 

cells, and the resistance of the battery is the sum 
of the resistances of all the cells. High electro- 
motive forces or ^' pressures " capable of over- 
coming high resistances outside the battery can 
be obtained in this way. 

Figure 14 shows how the zincs are joined '^ in 
parallel," the zinc or negative pole of one being 
connected by wire to the zinc or negative pole of 
the rest, and all the copper or positive poles to- 
gether. This arrangement does not increase the 
electromotive force, but diminishes the resistance. 
In fact, the battery is equivalent to a single cell 
having plates equal in area to the total area of all 
the plates. Although unable to overcome a high 
resistance, it can produce a large volume or quan- 
tity of electricity. 

Numerous voltaic combinations and varieties 
of cell have been found out. In general, where- 
ever two metals in contact are placed in a liquid 
which acts with more chemical energy on one 
than on the other, as sulphuric acid does on 
zinc in preference to copper, there is a develop- 
ment of electricity. Readers may have seen how 
an iron fence post corrodes at its junction with 
the lead that fixes it in the stone. This decay is 
owing to the wet forming a voltaic couple with 
the two dissimilar metals and rusting the iron. 
In the following list of materials, when any two 
in contact are plunged in dilute acid, that which 
is higher in the order becomes the positive plate 
or negative pole to that which is lower: — 



Positive. 


Iron. 


Silver. 


Zinc. 


Nickel. 


Gold. 


Cadmium. 


Bismuth. 


Platinum. 


Tin. 


Antimony. 


Graphite. 


Lead. 


Copper. 


Negative 



32 THE STORY OF ELECTRICITY. 

There being no chemical union between the 
hydrogen and copper in the zinc and copper 
couple, that gas accumulates on the surface of 
the copper plate, or is liberated in bubbles. Now, 
hydrogen is positive compared with copper, hence 
they tend to oppose each other in the combina- 
tion. The hydrogen diminishes the value of the 
copper, the current grows weaker, and the cell is 
said to ** polarise." It follows that a simple water 
cell is not a good arrangement for the supply of a 
steady current. 

The Daniell cell is one of the best, and gives a 
very constant current. In this battery the copper 
plate is surrounded by a solution of sulphate of 
copper [Cu SO^, which the hydrogen decomposes, 
forming sulphuric acid [H^SO^), thus taking itself 
out of the way, and leaving pure copper [Cu) to 
be deposited as a fresh surface on the copper 
plate. A further improvement is made in the 
cell by surrounding the zinc plate with a solution 
of sulphate of zinc [Zn SO4), which is a good con- 
ductor. Now, when the oxide of zinc is formed 
by the oxygen uniting with the zinc, the free sul- 
phuric acid combines with it, forming more sul- 
phate of zinc, and maintaining the conductivity of 
the cell. It is only necessary to keep up the sup- 
ply of zinc, water, and sulphate of copper to pro- 
cure a steady current of electricity. 

The Daniell cell is constructed in various 
ways. In the earlier models the two plates 
with their solutions were separated by a porous 
jar or partition, which allowed the solutions to 
meet without mixing, and the current to pass. 
Sawdust moistened with the solutions is some- 
times used for this porous separator, for instance, 
on board ships for laying submarine cables, 



THE ELECTRICITY OF CHEMISTRY. 



33 



where the rolling of the waves would blend the 
liquids. 

In the ''gravity" Daniell the solutions are 
kept apart by their specific gravities, yet mingle 
by slow diffusion. Figure 15 illustrates this com- 
mon type of cell, where 
Z is the zinc plate in a 
solution of sulphate of 
zinc, and C is the copper 
plate in a solution of sul- 
phate of copper, fed by 
crystals of the '' blue vit- 
riol." The wires to con- 
nect the plates are shown 
at IF JF. It should be no- 
ticed that the zinc is cast 
like a wheel to expose a 
larger surface to oxida- 
tion, and to reduce the 
resistance of the cell, 
thus increasing the yield 
of current. The extent 
of surface is not so important in the case of the 
copper plate, which is not acted on, and in this case 
is merely a spiral of wire, helping to keep the solu- 
tions apart and the crystals down. The Daniell 
cell is much employed in telegraphy. The Bunsen 
cell consists of a zinc plate in sulphuric acid, and a 
carbon plate in nitric acid, with a porous separator 
between the liquids. During the action of the cell, 
hydrogen, which is liberated at the carbon plate, 
is removed by combining with the nitric acid. 
The Grove cell is a modification of the Bunsen, 
with platinum instead of carbon. The Smee cell 
is a zinc plate side by side with a ''platinised " 
silver plate in dilute sulphuric acid. The silver 
3 




Fig. 15.— a Daniell Cell. 



34 



THE STORY OF ELECTRICITY. 



is coated with rough platinum to increase the sur- 
face and help to dislodge the hydrogen as bub- 
bles and keep it from polarising the cell. The 
Bunsen, Grove, and Smee batteries are, however, 
more used in the laboratory than elsewhere. 

The Leclanche is a fairly constant cell, which 
requires little attention. It '' polarises " in action 
but soon regains its normal strength when allowed 
to rest, and hence it is useful for working electric 
bells and telephones. As shown in figure i6, it 
consists of a zinc rod with its connecting wire Z, 
and a carbon plate C with its binding screw, be- 
tween two cakes J/ J/ of 
a mixture of black oxide 
of manganese, sulphur, 
and carbon, plunged in a 
solution of sal ammoniac. 
The oxide of manganese 
relieves the carbon plate 
of its hydrogen. The 
strength of the solution 
is maintained by spare 
crystals of sal ammoniac 
lying on the bottom of 
the cell, which is closed 
to prevent evaporation, 
but has a venthole for 
the escape of gas. 
The Bichromate of Potash cell polarises more 
than the Leclanche, but yields a more powerful 
current for a short time. It consists, as shown 
in figure 17, of a zinc plate Z between two carbon 
plates C C immersed in a solution of bichromate 
of potash, sulphuric acid (vitriol), and water. The 
zinc is always lifted out of the solution when the 
cell is not in use. The gas which collects in the 




Fig. 16.— The Leclanche Cell. 



THE ELECTRICITY OF CHEMISTRY. 



35 



carbons, and weakens the cell, can be set free by 
raising the plates out of the liquid when the cell 
is not wanted. Stirring the solution has a similar 
effect, and sometimes the constancy of the cell is 
maintained by a circulation of the liquid. In 
Fuller's bichromate cell the zinc is amalgamated 
with mercury, which is kept in a pool beside it 
by means of a porous pot. 

De la Rue's chloride of silver cell (hg. i8) 

is, from its 

constancy and __ 

small size, well 

adapted for 

medical and 

ing purposes. 

*' plates "are a 



test- 

The 

little 

rod or pencil of zinc 

Z, and a strip or wire 

of silver S, coated 

with chloride of sil- 
ver and sheathed 

in parchment paper. 

They are plunged 

in a solution of 

ammonium chloride 

A, contained in a 
glass phial or beaker, which is closed to sup- 
press evaporation. A tray form of the cell is 
also made by laying a sheet of silver foil on 
the bottom of the shallow jar, and strewing it 
with dry chloride of silver, on which is laid 
a jelly to support the zinc plate. The jelly is 
prepared by mixing a solution of chloride of am- 
monium with '' agar-agar," or Ceylon moss. This 
type permits the use of larger plates, and adapts 
the battery for lighting small electric lamps. 





Fig. 17.— The 
Bichromate Cell. 



Fig. 18. 

The Chloride of 

Silver Cell. 



36 THE STORY OF ELECTRICITY. 

Skrivanoff has modified the De la Rue cell by 
substituting a solution of caustic potash for the 
ammonium chloride, and his battery has been 
used for " star 'Mights, that is to say, the tiny 
electric lamps of the ballet. The Schanschieff 
battery, consisting of zinc and carbon plates in 
a solution of basic sulphate of mercury, is suit- 
able for reading, mining, and other portable 
lamps. 

The Latimer Clark ^* standard " cell is used by 
electricians in testing, as a constant electromotive 
force. It consists of a pure zinc plate separated 
from a pool of mercury by a paste of mercurous 
proto-sulphate and saturated solution of sulphate 
of zinc. Platinum wires connect with the zinc 
and mercury and form the poles of the battery, 
and the mouth of the glass cell is plugged with 
solid paraffin. As it is apt to polarise, the cell 
must not be employed to yield a current, and 
otherwise much care should be taken of it. 

Dry cells are more cleanly and portable than 
wet, they require little or no attention, and are 
well suited for household or medical purposes. 
The zinc plate forms the vessel containing the 
carbon plate and chemical reagents. Figure 19 
represents a section of the '' E. C. C." variety, 
where Z is the zinc standing on an insulating 
sole /, and fitted with a connecting wire or 
terminal 7^('— ), which is the negative pole. The 
carbon C is embedded in black paste M, chiefly 
composed of manganese dioxide, and has a bind- 
ing screw or terminal T (+), which is the posi- 
tive pole. The black paste is surrounded by a 
white paste Z, consisting mainly of lime and sal- 
ammoniac. There is a layer of silicate cotton 
6* C above the paste, and the mouth is sealed with 



THE ELECTRICITY OF CHEMISTRY. 



37 



black pitch P, through which a waste-tube W T 
allows the gas to escape. 

The Hellesen dry cell is like the '' E. C. C," 
but contains a 

hollow carbon, T(-4-) C 

and is packed 
with sawdust 
in a millboard 
case. The Le- 
clanche-Barbier 
dry cell is a 
modification of 
the Leclanche 
wet cell, having 
a paste of sal- 
ammoniac in- 
stead of a so- 
lution. 

All the fore- 
going cells are 
called ^^ prima- 
ry," because 
they are gener- 
ators of electri- 
city. There are, however, batteries known as '' sec- 
ondary," which store the current as the Leyden 
jar stores up the discharge from an electrical 
machine. 

In the action of a primary cell, as we have 
seen, water is split into its constituent gases, 
oxygen and hydrogen. Moreover, it was dis- 
covered by Carlisle and Nicholson in the year 
1800 that the current of a battery could de- 
compose water in the outer part of the circuit. 
Their experiment is usually performed by the 
apparatus shown in figure 20, which is termed a 




Fig. 19.— The E. C. C. Dr>' Cell. 



38 



THE STORY OF ELECTRICITY. 



voltameter, and consists of a glass vessel V, con- 
taining water acidulated with a little sulphuric 
acid to render it a better conductor, and two glass 
test-tubes OZT inverted over two platinum strips 
or electrodes, which rise up from the bottom of 
the vessel and are connected underneath it to 
wires from the positive and negative poles of the 
battery C Z. It will be understood that the cur- 




FiG. 20. — The Voltameter. 



rent enters the water by the positive electrode, 
and leaves it by the negative electrode. 

When the power of the battery is sufficient the 
water in the vessel is decomposed, and oxygen 
being the negative element, collects at the posi- 
tive foil or electrode, which is covered by the 
tube O. The hydrogen, on the other hand, being 
positive, collects at the negative foil under the 
tube H, These facts can be proved by dipping 
a red-hot wick or taper into the gas of the tube 
O and seeing it blaze in presence of the oxygen 
which feeds the combustion, then dipping the 



THE ELECTRICITY OF CHEMISTRY. 39 

lighted taper into the gas of the tube H and 
watching it burn with the blue flame of hydro- 
gen. The volume of gas at the cathode or nega- 
tive electrode is always twice that at the anode or 
positive electrode, as it should be according to 
the known composition of water. 

Now, if we disconnect the battery and join the 
two platinum electrodes of the voltameter by a 
wire, we shall find a current flowing out of the 
voltameter as though it were a battery, but in 
the reverse direction to the original current which 
decomposed the water. This ** secondary " or re- 
acting current is evidently due to the polar- 
isation " of the foils — that is to say, the electro- 
positive and electro-negative gases collected on 
them. 

Professor Groves constructed a gas battery 
on this principle, the plates being of platinum 
and the two gases surrounding them oxygen and 
hydrogen, but the most useful development of it 
is the accumulator or storage battery. 

The first practicable secondary battery of 
Gaston Plante w^as . made of sheet lead plates 
or electrodes, kept apart by linen cloth soaked 
in dilute sulphuric acid, after the manner of 
Volta's pile. It was '' charged " by connecting 
the plates to a primary battery, and peroxide of 
lead {Pb O2) was formed on one plate and spongy 
lead [Fb) on the other. When the charging cur- 
rent was cut off the peroxide plate became the 
positive and the spongy plate the negative pole 
of the secondary cell. 

Faure improved the Plante cell by adding a 
paste of red lead or minium {Fb2 O^ and dilute 
sulphuric acid {H^ '^^4)1 by which a large quan- 
tity of peroxide and spongy lead could be formed 



40 



THE STORY OF ELECTRICITY. 



on the plates. Sellon and Volckmar increased 
its efficiency by putting the paste into holes cast 
in the lead. The " E. P. S." accumulator of the 
Electrical Power Storage Company is illustrated 
in figure 21, and consists of a glass or teak box 




Fig. 21.— The E. P. S. Accumulator. 

containing two sets of leaden grids perforated 
with holes, which are primed with the paste and 
'Steeped in dilute sulphuric acid. Alternate grids 
are joined to the poles of a charging battery or 
generator, those connected to the positive pole 
being converted into peroxide of lead and the 
others into spongy lead. The terminal of the 
peroxide plates, being the positive pole of the 
accumulator, is painted red, and that of the 
spongy plates or negative pole black. Accumu- 
lators of this kind are highly useful as reservoirs 
of electricity for maintaining the electric light, or 
working electric motors in tramcars, boats, and 
other carriages. 



THE ELECTRICITY OF HEAT. 41 

CHAPTER III. 

THE ELECTRICITY OF HEAT. 

In the year 182 1 Professor Seebeck, of Ber- 
lin, discovered a third source of electricity. Volta 
had found that two dissimilar metals in contact 
will produce a current by chemical action, and 
Seebeck showed that heat might take the place 
of chemical action. Thus, if a bar of antimony 
A (fig. 22) and a bar of bismuth B are in contact 
at one end, and the junc- 
tion is heated by a spirit 
lamp to a higher tempera- 
ture than the rest of the 
bars, a difference in their 
electric state or potential 
will be set up, and if the 
other ends are joined by a 
wire W, a current will flow^ x^,^ ^^ 

11 • rT^^ ^' rlG. 22. 

through the wire. The dl- a Thermo-electric Couple. 

rection of the current, in- 
dicated by the arrow, is from the bismuth to the 
antimony across the joint, and from the antimony 
to the bismuth through the external wire. This 
combination, which is called a '' thermo-electric 
couple," is clearly analogous to the voltaic couple, 
with heat in place of chemical affinity. The direc- 
tion of the current within and without the couple 
shows that the bismuth is positive to the antimony. 
This property of generating a current of elec- 
tricity by contact under the influence of heat is 
not confined to bismuth and antimony, or even 
to the metals, but is common to all dissimilar 
substances in their degree. In the following list 
of bodies each is positive to those beneath it, 




42 THE STORY OF ELECTRICITY. 

negative to those above it, and the further apart 
any two are in the scale the greater the effect. 
Thus bismuth and antimony give a much stronger 
current with the same heating than copper and 
iron. Bismuth and selenium produce the best 
result, but selenium is expensive and not easy to 
manipulate. Copper and German silver will make 
a cheap experimental couple: — 
Positive. 

Bismuth. 

Cobalt. 

Potassium. 

Nickel. 

Sodium. 

Lead. 

Tin. 

Copper. 

Platinum. 

Silver. 

Zinc. 

Cadmium. 

Arsenic. 

Iron. 

Red phosphorus. 

Antimony. 

Tellurium. 

Selenium. 
Negative. 
Other things being equal, the hotter the joint 
in comparison with the free ends of the bars the 
stronger the current of electricity. Within cer- 
tain limits the current is, in fact, proportional to 
this difference of temperature. It always flows 
in the same direction if the joint is not over- 
heated, or, in other words, raised above a certain 
temperature. 



THE ELECTRICITY OF HEAT. 43 

The electromotive force and current of a 
thermo-electric couple is very much smaller than 
that given by an ordinary voltaic cell. We can, 
however, multiply the effect by connecting a 
number of pairs together, and so forming a pile 
or battery. Thus figure 23 shows three couples 
joined ^* in series," the positive pole of one being 
connected to the negative pole of the next. Now, 
if all the junctions on the left are hot and those 
on the right are cool, we will get the united effect 
of the whole, and the total 
current will flow through 
the wire IV, joining the ex- 
treme bars or positive and 
negative poles of the bat- 
tery. It must be borne in 
mind that although the bis- 
muth and antimony of this 
thermo-electric battery, like 
the zinc and copper of ^_ ^ , ^ . 

, , . ^/ . Fig, 23. — ^Thermo-electnc 

the voltaic or chemiCO- Couples in Series. 

electric battery, are re- 
spectively positive and negative to each other, 
the poles or wires attached to these metals are, 
on the contrary, negative and positive. This 
peculiarity arises from the current starting be- 
tween the bismuth and antimony at the heated 
junction. 

The internal resistance of a '' thermo-electric 
pile " is, of course, very slight, the metals being 
good conductors, and this fact gives it a certain 
advantage over the voltaic battery. Moreover, 
it is cleaner and less troublesome than the chemi- 
cal battery, for it is only necessary to keep up 
the required difference of temperature between 
the hot and cold junctions in order to get a 




44 



THE «TORY OF ELECTRICITY. 



steady current. No solutions or salts are re- 
quired, and there appears to be little or no waste 
of the metals. It is important, however, to avoid 
sudden heating and cooling of the joints, as this 
tends to destroy them. 

Clammond, Giilcher, and others have con- 
structed useful thermo-piles for practical pur- 
poses. Figure 24 illus- 
trates a Clammond ther- 
mo-pile of 75 couples or 
elements. The metals 
forming these pairs are 
an alloy of bismuth and 
antimony for one and 
iron for the other. 
Prisms of the alloy are 
cast on strips of iron 
to form the junctions. 
They are bent in rings, 
the junctions in a series 
making a zig-zag round 
the circle. The rings 
other in a cylinder of 
couples, and the inner junctions are heated by 
a Bunsen gas-burner in the hollow core of the 
battery. A gas-pipe seen in front leads to the 
burner, and the wires ^W^ connected to the ex- 
treme bars or poles are the electrodes of the pile. 
Thermo-piles are interesting from a scientific 
point of view as a direct means of transforming 
heat into electricity. A sensitive pile is also a 
delicate detector of heat by virtue of the current 
set up, w^hich can be measured with a galvan- 
ometer or current meter. Piles of antimony and 
bismuth are made which can indicate the heat 
of a lighted match at a distance of several 




Fig. 24. 
A Thermo-electric Pile. 



are built one over the 



THE ELECTRICITY OF HEAT. 45 

yards, and even the radiation from certain of the 
stars. 

Thermo-batteries have been used in France 
for working telegraphs, and they are capable of 
supplying small installations of the electric light 
or electric motors for domestic purposes. 

The action of the thermo-pile, like that of a 
voltaic cell, can be reversed. By sending a cur- 
rent through the couple from the antimony to the 
bismuth we shall find the junction cooled. This 
" Peltier effect," as it is termed, after its dis- 
coverer, has been known to freeze water, but no 
practical application has been made of it. 

A very feeble thermo-electric effect can be 
produced by heating the junction of two different 
pieces of the same substance, or even by making 
one part of the same conductor hotter than 
another. Thus a sensitive galvanometer will 
show a weak current if a copper wnre connected 
in circuit with it be warmed at one point. More- 
over, it has been found by Lord Kelvin that if an 
iron wire is heated at any point, and an electric 
current be passed through it, the hot point will 
shift along the wire in a direction contrary to 
that of the current. 



CHAPTER IV. 

THE ELECTRICITY OF MAGNETISM. 

We have already seen how electricity was first 
produced by the simple method of rubbing one 
body on another, then by the less obvious means 
of chemical union, and next by the finer agency 



46 THE STORY OF ELECTRICITY. 

of heat. In all these, it will be observed, a sub- 
stantial contact is necessary. We have now to 
consider a still more subtle process of generation, 
not requiring actual contact, which, as might be 
expected, was discovered later, that, mainly 
through the medium of magnetism. 

The curious mineral which has the property 
of attracting iron was known to the Chinese 
several thousand years ago, and certainly to the 
Greeks in the times of Thales, who, as in the 
case of the rubbed amber, ascribed the property 
to its possession of a soul. 

Lodestone, a magnetic oxide of iron [Fe^ O^^ 
is found in various parts of China, especially at 
T'szchou in Southern Chihli, which was formerly 
known as the ^' City of the Magnet." It was 
called by the Chinese the love-stone or thsu-chy, 
and the stone that snatches iron or ny-thy-chy, 
and perchance its property of pointing out the 
north and south direction was discovered by drop- 
ping a light piece of the stone, if not a sewing 
needle made of it, on the surface of still water. 
At all events, we read in Pere Du Halde's Descrip- 
tion de la Chine^ that sometime in or about the year 
2635 B. c. the great Emperor Hoang-ti, having lost 
his way in a fog whilst pursuing the rebellious 
Prince Tchiyeou on the plains of Tchou-lou, con- 
structed a chariot which showed the cardinal 
points, thus enabling him to overtake and put the 
prince to death. 

A magnetic car preceded the Emperors of 
China in ceremonies of state during the fourth 
century of our era. It contained a genius in a 
feather dress who pointed to the south, and was 
doubtless moved by a magnet floating in water 
or turning on a pivot. This rude appliance was 



THE ELECTRICITY OF MAGNETISM. 47 

afterwards refined into the needle compass for 
guiding mariners on tlie sea, and assisting the 
professors of feng-shui or geomancy in their 
magic rites. 

Magnetite was also found at Heraclea in 
Lydia, and at Magnesium on the Meander or 
Magnesium at Sipylos, all in Asia Minor. It was 
called the " Heraclean Stone" by the people, but 
came at length to bear the name of ^* Magnet " 
after the city of Magnesia or the mythical shep- 
herd Magnes, who was said to have discovered it 
by the attraction of his iron crook. 

The ancients knew that it had the power of 
communicating its attractive property to iron, for 
we read in Plato's " Ion " that a number of iron 
rings can be supported in a chain by the Hera- 
clean Stone. Lucretius also describes an experi- 
ment in which iron filings are made to rise up 
and '* rave " in a brass basin by a magnet held 
underneath. We are told by other writers that 
images of the gods and goddesses were suspended 
in the air by lodestone in the ceilings of the 
temples of Diana of Ephesus, of Serapis at Alex- 
andria, and others. It is surprising, however, 
that neither the Greeks nor Romans, with all 
their philosophy, would seem to have discovered 
its directive property. 

During the dark ages pieces of lodestone 
mounted as magnets were employed in the ^' black 
arts." A small natural magnet of this kind is 
shown in figure 25, w^here L is the stone shod 
with two iron '' pole-pieces," which are joined by 
a '* keeper " A or separable bridge of iron carry- 
ing a hook for supporting weights. 

Apparently it was not until the twelfth cen- 
tury that the compass found its way into Europe 



48 



THE STORY OF ELECTRICITY. 



from the East. In the Landnammabok of Ari 
Frode, the Norse historian, we read that Flocke 
Vildergersen, a renowned viking, sailed from 
Norway to discover Iceland in the year 868, and 
took with him two ravens as guides, for in those 
days the '^ seamen had no lodestone (that is, no 
lidar stein, or leading stone) in the northern 
countries." The Bible, a poem of Guiot de Pro- 
vins, minstrel at the court of Barbarossa, which 
was written in or about the year 1190, contains 
the first mention of the magnet in the West. 
Guiot relates how mariners have an *' art which 
cannot deceive" of finding the position of the 
polestar, that does not move. 
After touching a needle with 
the magnet, ^' an ugly brown 
stone which draws iron to 
itself," he says they put the 
needle on a straw and float it 
on water so that its point 
turns to the hidden star, and 
enables them to keep their 
course. Arab traders had 
probably borrowed the float- 
ing needle from the Chinese, 
for Bailak Kibdjaki, author 
of the Merchant's Treasm^e^ 
written in the thirteenth cen- 
tury, speaks of its use in the 
Syrian sea. The first Cru- 
saders were probably instru- 
mental in bringing it to France, at all events 
Jacobus de Vitry (1204-15) and Vincent de Beau- 
vais (1250) mention its use, De Beauvais calling 
the poles of the needle by the Arab words aphron 
and zohron. 




Fig. 25. 
A Natural Magnet. 



THE ELECTRICITY OF MAGNETISM. 49 

Ere long the needle was mounted on a pivot 
and provided with a moving card showing the 
principal directions. The variation of the needle 
from the true north and south was certainly 
known in China during the twelfth, and in Europe 
during the thirteenth century. Columbus also 
found that the variation changed its value as he 
sailed towards America on his memorable voyage 
of 1492. Moreover, in 1576, Norman, a compass 
maker in London, showed that the north-seeking 
end of the needle dipped below the horizontal. 

In these early days it was supposed that lode- 
stone in the pole-star, that is to say, the ** lode- 
star " of the poets or in mountains of the far 
north, attracted the trembling needle ; but in the 
year 1600, Dr. Gilbert, the founder of electric 
science, demonstrated beyond a doubt that the 
whole earth was a great magnet. A magnet, as is 
well known, has, like an electric battery, always 
two poles or centres of attraction, which are situ- 
ated near its extremities. Sometimes, indeed, 
when the magnet is imperfect, there are ^^ conse- 
quent poles " of weaker force between them. 
One of the poles is called the ^^ north," and the 
other the '* south," because if the magnet were 
freely pivotted like a compass needle, the former 
would turn to the north and the latter to the 
south. 

Either pole will attract iron, but soft or an- 
nealed iron does not retain the magnetism nearly 
so well as steel. Hence a boy's test for the steel 
of his knife is only efficacious when the blade 
itself becomes magnetic after being touched with 
the magnet. A piece of steel is readily magnet- 
ised by stroking it from end to end in one direc- 
tion with the pole of a magnet, and in this way 
4 



so 



THE STORY OF ELECTRICITY. 



compass needles and powerful bar magnets can 
be made. 

The poles attract iron at a distance by ''in- 
duction," just as a charge of electricity, be it 
positive or negative, will attract 
a neutral pith ball; and Dr. Gil- 
bert showed that a north pole 
always repels another north pole 
and attracts a south pole, while, 
on the other hand, 
a south pole always 
repels a south pole 
and attracts a north 
pole. This can be 
proved by suspend- 
ing a magnetic nee- 
dle like a pithball, 
and approaching an- 
other towards it, as 
illustrated in figure 
26, where the north 
S. Obviously there 
magnetic poles, as 




Fig. 26. 



pole JV attracts the south 
are two opposite kinds of 

of electricity, which always appear together, and 
like magnetic poles repel^ unlike magnetic poles at- 
tract each other. 

It follows that the magnetic pole of the 
compass needle which turns to the north must 
be unlike the north and like the south magnetic 
pole of the earth. Instead of calling it the 
" north," it would be less confusing to call it 
the *Vnorth-seeking " pole of the needle. 

Gilbert made a ''terella," or miniature of the 
earth, as a magnet, and not only demonstrated 
how the compass needle sets along the lines 
joining the north and south magnetic poles, but 



THE ELECTRICITY OF MAGNETISM. 51 

explained the variation and the dip. He im- 
agined that the magnetic poles coincided with 
the geographical poles, but, as a matter of fact, 
they do not, and, moreover, they are slowly 
moving round the geographical poles, hence the 
decliiiation of the needle, that is to say its angle 
of divergence from the true meridian or north 
and south line, is gradually changing. The 
north magnetic pole of the earth was actually 
discovered by Sir John Ross north of British 
America, on the coast of Boothia (latitude 70^5' 
N., longitude 96° 46' W. ), where, as foreseen, the 
needle entirely lost its directive property and 
stood upright, or, so to speak, on its head. The 
south magnetic pole lies in the Prince Albert 
range of Victoria Land, and was almost reached 
by Sir James Clark Ross. 

The magnetism of the earth is such as might 
be produced by a powerful magnet inside, but its 
origin is unknown, although there is reason to 
believe that masses of lodestone or magnetic iron 
exist in the crust. Coulomb found that not only 
iron, but all substances are more or less magnetic, 
and Faraday showed in 1845 ^^at while some are 
attracted by a magnet others are repelled. The 
former he called paraviagiietic and the latter dia- 
magnetic bodies. 

The following is a list of these : — 

Pa ra magnetic. Diamagnetic. 

Iron. Bismuth. 



Nickel. 



Phosphorus. 
Antimony. 

Cobalt. 2:inc. 

Mercury. 
Aluminium. Lead. 



52 THE STORY OF ELECTRICITY. 

Manganese. Silver. 

Chromium. ^^PP^"' 

_ . Gold. 

Cerium. Water. 

Titanium. Alcohol. 

Platinum. Tellurium. 

Many ores and Selenium. 

1.- r ^u Sulphur. 

salts of the Thallium. 

above metals. Hydrogen. 

Oxygen. Air. 

We have theories of magnetism that reduce 
it to a phenomenon of electricity, though we are 
ignorant of the real nature of both. If we take 
a thin bar magnet and break it in two, we find 
that we have now two shorter magnets, each with 
its "north" and "south" poles, that is to say, 
poles of the same kind as the south and north 
magnetic poles of the earth. If we break each of 
these again, we get four smaller magnets, and we 
can repeat the process as often as we like. It is 
supposed, therefore, that every atom of the bar is 
a little magnet in itself having its two opposite 
poles, and that in magnetising the bar we have 
merely partially turned all these atoms in one 
direction, that is to say, with their north poles 
pointing one way and their south poles the other 
way, as shown in figure 27. The polarity of the 
bar only shows itself at the ends, where the molec- 
ular poles are, so to speak, free. 

There are many experiments which support 
this view. For example, if we heat a magnet 
red hot it loses its magnetism, perhaps because 
the heat has disarranged the particles and set 
the molecular poles in all directions. Again, if 



THE ELECTRICITY OF MAGNETISM. 53 

we magnetise a piece of soft iron we can destroy 
its magnetism by striking it so as to agitate its 
atoms and throw them out of line. In steel, 
which is iron with a small admixture of carbon, 
the atoms are not so free as in soft iron, and 
hence, while iron easily loses its magnetism, steel 



UllUllllllJUL ' llLJiUllIllLJllI^ 



m am oiiD ODD CMD oniiD OHD am 



rmnii mmi ininnMinimrTiimniinnni 



retains it, even under a shock, but not under a 
cherry red-heat. Nevertheless, if we put the 
atoms of soft iron under a strain by bending it, 
we shall find it retain its magnetism more like a 
bit of steel. 

It has been found, too, that the atoms show 
an indisposition to be moved by the magnetising 
force which is known as hysteresis. They have a 
certain inertia, which can be overcome by a slight 
shock, as though they had a difficulty of turning 
in the ranks to take up their new positions. 
Even if this molecular theory is true, however, 
it does not help us to explain why a molecule of 
matter is a tiny magnet. We have only pushed 
the mystery back to the atom. Something more 
is wanted, and electricians look for it in the con- 
stitution of the atom, and in the luminiferous 
ether which is believed to surround the atoms of 
matter, and to propagate not merely the waves 
of light, but induction from one electrified body 
to another. 

We know in proof of this ethereal action that 
the space around a magnet is magnetic. Thus, 
if we lay a horse-shoe magnet on a table and 



54 



THE STORY OF ELECTRICITY. 



sprinkle iron filings round it, they will arrange 
themselves in curving lines between the poles as 
shown in figure 28. Each filing has become a 

little magnet, and these 
set themselves end to 
end as the molecules in 
the metal are supposed 
to do. The "field" 
about the magnet is re- 
plete with these lineSp 
which follow certain 
curves depending on the 
arrangement of the poles. 
In the horse-shoe magnet, 
as seen, they chiefly issue 
from one pole and sweep 
round to the other. 
They are never broken, 
and apparently they are 
lines of stress in the 
circumambient ether. A 
pivoted magnet tends to 
range itself along these 
lines, and thus the com- 
pass guides the sailor on 
the ocean by keeping itself in the line between 
the north and south magnetic poles of the earth. 
Faraday called them lifies of magnetic force^ and 
said that the stronger the magnet the more of 
these lines pass through a given space. Along 
them *^ magnetic induction " is supposed to be 
propagated, and a magnet is thus enabled to attract 
iron or any other magnetic substance. The pole 
induces an opposite pole to itself in the nearest 
part of the induced body and a like pole in the 
remote part. Consequently, as unlike poles at- 




FlG. 28. 



THE ELECTRICITY OF MAGNETISM. 



55 



tract and like repel, the soft iron is attracted by 
the inducing pole much as a pithball is attracted 
by an electric charge. 

The resemblances of electricity and magnet- 
ism did not escape attention, and the derangement 
of the compass needle by the lightning flash, for- 
merly so disastrous at sea, pointed to an intimate 
connection between them, which was ultimately 
disclosed by Professor Oersted, of Copenhagen, 
in the year 1820. Oersted was on the outlook 
for the required clue, and a happy chance is said 
to have rewarded him. His experiment is shown 
in figure 29, where a wire conveying a current of 




Fig. 29. 



electricity flowing in the direction of the arrow 
is held over a pivoted magnetic needle so that 
the current flows from south to north. The 
needle will tend to set itself at right angles to 
the wire, its north or north-seeking pole moving 
towards the west. If the direction of the current 
is reversed, the needle is deflected in the opposite 



56 



THE STORY OF ELECTRICITY. 



direction, its north pole moving towards the east. 
Further, if the wire is held below the needle, in 
the first place, the north pole will turn towards 
the east, and if the current be reversed it will 
move towards the west. 

The direction of a current can thus be told 
with the aid of a compass needle. When the wire 
is wound many times round the needle on a bob- 
bin, the whole forms what is called a galvano- 
scope, as shown in figure 30, where N is the 




Fig. 30. — The Galvanoscope. 



needle and B the bobbin. When a proper scale 
is added to the needle by which its deflections 
can be accurately read, the instrument becomes a 
current measurer or galvanometer, for within cer- 
tain limits the deflection of the needle is propor- 
tional to the strength of the current in the wire. 

A rule commonly given for remembering the 
movement of the needle is as follows : — Imagine 
yourself laid along the wire so that the current 
flows from your feet to your head ; then if you 
face the needle you will see its north pole go to 
the left and its south pole to the right. I find it 
simpler to recollect that if the current flows from 
your head to your feet a north pole will move 
round you from left to right in front. Or, again, 
if a current flows from north to south, a north 




THE ELECTRICITY OF MAGNETISM. 57 

pole will move round it like the sun round the 
earth. 

The influence of the current on the needle 
implies a magnetic action, and if we dust iron 
filings around the wire we shall find they cHng to 
it in concentric layers, showing that circular lines 
of magnetic force enclose it like the water waves 
caused by a stone dropped into a pond. Figure 
31 represents the section of a wire carrying a 
current, with the iron filmgs 
arranged in circles round it. 
Since a magnetic pole tends to 
move in the direction of the 
lines of force, we now see why 
a north or south pole tends to 
move round a current, and why fig. 31. 

a compass needle tries to set 
itself at right angles to a current, as in the original 
experiment of Oersted. The needb, having two 
opposite poles, is pulled in opposite directions by 
the lines, and being pivoted, sets itself tangenti- 
cally to them. Were it free and flexible, it would 
curve itself along one of the lines. Did it consist 
of a single pole, it would revolve round the wire. 

Action and re-action are equal and opposite, 
hence if the needle is fixed and the wire free the 
current will move round the magnet ; and if 
both are free they will circle round each other. 
Applying the above rule we shall find that when 
the north pole moves from left to right the cur- 
rent moves from right to left. Ampere of Paris, 
following Oersted, promptly showed that two 
parallel wires carrying currents attracted each 
other when the currents flowed in the same direc- 
tion, and repelled each other when they flowed in 
opposite directions. Thus, in figure ^y^^ if A and 



58 



THE STORY OF ELECTRICITY. 



B are the two parallel wires, and A is mounted 
on pivots and free to move in liquid " contacts" 
of mercury, it will be attracted or repelled by B 
according as the two currents flow in the same or 
in opposite directions. If the wires cross each 
other at right angles there is no attraction or re- 
pulsion. If they cross at an acute angle, they 
will tend to become parallel like two compass 




B 




Fig. 32. 

needles, when the currents are in one direction, 
and to open to a right angle and close up the 
other way when the currents are in opposite 
directions, always tending to arrange themselves 
parallel and flowing in the same direction. These 



THE ELECTRICITY OF MA(}NETISM. 59 

effects arise from the circular lines of force 
around the wire. When the currents are similar 
the lines act as unlike magnetic poles and attract, 
but when the currents are dissimilar the lines act 
as like magnetic poles and repel each other. 

Another important discovery of Ampere is 
that a circular current behaves like a magnet ; 
and it has been suggested by him that the atoms 
are magnets because each has a circular current 
flowing round it. A series of circular currents, 
such as the spiral 6' in figure ;^;^ gives, when con- 
nected to a battery C Z, is in fact a skeleton 




Fig. 33. 

electro-magnet having its north and south poles at 
the extremities. If a rod or core of soft iron / 
be suspended by fibres from a support, it will be 
sucked towards the middle of the coil as into a 
vortex, by the circular magnetic lines of every 
spire or turn of the coil. Such a combination is 
sometimes called a solenoid, and is useful in 
practice. 



6o 



THE STORY OF ELECTRICITV. 



When the core gains the interior of the coil it 
becomes a veritable electromagnet, as found by 
Arago, having a north pole at one end and a 
south pole at the other. Figure 34 illustrates a 
common poker magnetised in the same way, and 
supporting nails at both ends. The poker has 




Fig. 34. 

become the core of the electromagnet. On re- 
versing the direction of the current through the 
spiral we reverse the poles of the core, for the 
poker being of soft or wrought iron, does not 
retain its magnetism like steel. If we stop the 
current altogether it ceases to be a magnet, and 
the nails will drop away from it. 

Ampere's experiment in figure 32 has shown us 
that two currents, more or less parallel, influence 
each other; but in 1831 Professor Faraday of the 
Royal Institution, London, also found that when 
a current is started and stopped in a wire, it in- 
duces a momentary and opposite current in a 
parallel wire. Thus, if a current is started in the 
wire B (fig. 32) in direction of the arrow, it will 
induce or give rise to a momentary current in 
the wire A^ flowing in a contrary direction to 
itself. Again, if the current in B be stopped^ a 
momentary current is set up in the wire A in a. 
direction the same as that of the exciting current 



THE ELECTRICITY OF MAGNETISM. 



6l 



in B. While the current in B is quietly flowing 
there is no induced current in A ; and it is only 
at the start or the stoppage of the inducing or 
primary current that the induced or secondary cur- 
rent is set up. Here again we have the influence 
of the magnetic field around the wire conveying 
a current. 

This is the principle of the '' induction coil " 
so much employed in medical electricity, and of 
the '' transformer " or '^ converter " used in electric 
illumination. It consists essentially, as shown in 
figure II, of two coils of wire, one enclosing the 
other, and both parallel or concentric. The inner 



t7 ?■, 




Fig. 35. 

or primary coil /^ C is of short thick wire of low 
resistance, and is traversed by the inducing cur- 
rent of a battery B. To increase its inductive 
effect a core of soft iron / C occupies its middle. 
The outer or secondary coil 6* C is of long thin 
wire terminating in two discharging points D^ D^. 
An interruptor or hammer ''key" interrupts or 
*' makes and breaks" the circuit of the primary 



62 THE STORY OF ELECTRICITY. 

coil very rapidly, so as to excite a great many 
induced currents in the secondary coil per second, 
and produce energetic sparks between the ter- 
minals D^ D^' The interrupter is actuated auto- 
matically by the magnetism of the iron core / C, 
for the hammer H has a soft iron head which is 
attracted by the core when the latter is magnet- 
ised, and being thus drawn away from the con- 
tact screw C S the circuit of the primary is 
broken, and the current is stopped. The iron 
core then ceases to be a magnet, the hammer H 
springs back to the contact screw, and the cur- 
rent again flows in the primary circuit only to be 
interrupted again as before. In this way the 
current in the primary coil is rapidly started and 
stopped many times a second, and this, as we 
know, induces corresponding currents in the sec- 
ondary which appear as sparks at the discharging 
points. The effect of the apparatus is enhanced 
by interpolating a '* condenser" C C in the pri- 
mary circuit. A condenser is a form of Leyden 
jar, suitable for current electricity, and consists 
of layers of tinfoil separated from each other by 
sheets of paraffin paper, mica, or some other con- 
venient insulator, and alternate foils are con- 
nected together. The wires joining each set of 
plates are the poles of the condenser, and when 
these are connected in the circuit of a current 
the condenser is charged. It can be discharged 
by joining its two poles with a wire, and letting 
the two opposite electricities on its plates rush 
together. Now, the sudden discharge of the con- 
denser C C through the primary coil J^ C enhances 
the inductive effect of the current. The battery 
jB, here shown by the conventional symbol ^^ I | " 
where the thick dash is the negative and the thin 



THE ELECTRICITY OF MAGNETISM. 



63 



dash the positive pole, is connected between the 
terminals T^ To, and a commutator or pole-changer 
R, turned with a handle, permits the direction of 
the current to be reversed at will. 

Figure 36 represents the exterior of an ordi- 
nary induction coil of the Ruhmkorff pattern, 







Fig. 36. — The Induction Coil. 

with its two coils, one over the other C, its com- 
mutator R, and its sparkling points D^ Dc^, the 
whole being mounted on a mahogany base, which 
holds the condenser. 

The intermittent, or rather alternating, cur- 
rents from the secondary coil are often applied 
to the body in certain nervous disorders. When 
sent through glass tubes filled with rarefied gases, 
sometimes called " Geissler tubes," they elicit 
glows of many colours, vieing in beauty with the 
fleeting tints of the aurora polaris, which, indeed, 
is probably a similar effect of electrical discharges 
in the atmosphere. 

The action of the induction is reversible. We 
can not only send a current of low " pressure " 
from a generator of weak electromotive force 
through the primary coil, and thus excite a cur- 
rent of high pressure in the secondary coil, but 



64 THE STORY OF ELECTRICITY. 

we can send a current of high pressure through 
the secondary coil and provoke a current of low 
pressure in the primary coil. The transformer 
or converter, a modified induction coil used in dis- 
tributing electricity to electric lamps and motors, 




can not only transform a 
low pressure current into a 
high, but a high pressure 
current into a low. As the 
high pressure currents are fig. 37. 

best able to overcome the 
resistance of the wire conveying them, it is cus- 
tomary to transmit high pressure currents from 
the generator to the distant place where they 
are wanted by means of small wires, and there 
transform them into currents of the pressure 
required to light the lamps or drive the motors. 

We come now to another consequence of Oer- 
sted's great discovery, which is doubtless the 
most important of all, namely, the generation of 
electricity from magnetism, or, as it is usually 
called, magneto-electric induction. In the year 
183 1 the illustrious Michael Faraday further suc- 
ceeded in demonstrating that when a magnet M 
is thrust into a hollow coil of wire C, as shown in 
figure 37, a current of electricity is set up in the 
coil whilst the motion lasts. When the magnet is 
withdrawn again another current is induced in 



rw 



THE ELECTRICITY OF MAGNETISM. 65 

the reverse direction to the first. If the coil be 
closed through a small galvanometer G the move- 
ments of the needle to one side or the other will 
indicate these temporary currents. It follows 
from the principle of action and reaction that if 
the magnet is kept still and the coil thrust over it 
similar currents will be induced in the coil. All 
that is necessary is for the w4res to cut the lines 
of magnetic force around the magnet, or, in other 
words, the lines of force in a magnetic field. We 
have seen already that a wire conveying a current 
can move a magnetic pole, and we are therefore 
prepared to find that a magnetic pole moved near 
a wire can excite a current in it. 

Figure ;^S illustrates the conditions of this re- 
markable effect, where JV and 6" are two magnetic 
poles with lines of force 
between them, and JF is 
a wire crossing these 
lines at right angles, 

which is the best posi- r [— 1 

t i o n . I f , n o w , t h i s w i r e K L ;'.;;'.T.'.V. -. rr.**.V.".* .' '.'. ' 1 S 

be moved so as to sink ^ 

bodily through the pa- 
per away from the read- 
er, an electric current 
flowing in the direction Fig. 38. 

of the arrow will be in- 
duced in it. If, on the contrary, the wire be 
moved across the lines of force towards the read- 
er, the induced current wull flow oppositely to the 
arrow. Moreover, if the poles of the magnet A^ 
and 6" exchange places, the directions of the in- 
duced currents will also be reversed. This is the 
fundamental principle of the well-known dynamo- 
electric machine, popularly called a dynamo. 
5 



! 



66 



THE STORY OF ELECTRICITY. 



Again, if we send a current from some external 
source through the wire JV in the direction of the 
arrow, the wire will move of if se// 3.cvoss the lines 
of force away from the reader, that is to say, in 
the direction it would need to be moved in order 
to excite such a current ; and if, on the other 
hand, the current be sent through it in the re- 
verse direction to the arrow, it will move towards 
the reader. This is the principle of the equally 
well-known electric motor. Figure 39 shows a 
simple method of remembering these directions. 

Let the right hand rest 
on the north pole of a 
magnet and the fore- 
finger be extended in 
the direction of the 
lines of force, then 
the outstretched thumb 
will indicate the direc- 
tion in which the wire 
or conductor moves 
and the bent middle 
finger the direction of 
the current. These 
three digits, as will be noticed, are all at 
right angles to each other, and this relation is 
the best for inducing the strongest current in a 
dynamo or the most energetic movement of the 
conductor in an electric motor. 

Of course in a dynamo-electric generator 
the stronger the magnetic field, the less the 
resistance of the conductor, and the faster it 
is moved across the lines of force, that is 
to say, the more lines it cuts in a second the 
stronger is the current produced. Similarly 
in an electric motor, the stronger the current 




Fig. 39. 



THE ELECTRICITY OF MAGNETISM. 67 

and magnetic field the faster will the conductor 
move. 

The most convenient motion to give the con- 
ductor in practice is one of rotation, and hence 
the dynamo usually consists of a coil or series of 
coils of insulated wire termed the '' armature," 
which is mounted on a spindle and rapidly ro- 
tated in a strong magnetic field between the 
poles of powerful magnets. Currents are gener- 
ated in the coils, now in one direction then in 
another, as they revolve or cross different parts 
of the field ; and, by means of a device termed a 
commutator, these currents can be collected or 
sifted at will, and led away by wires to an electric 
lamp, an accumulator, or an electric motor, as 
desired. The character of the electricity is pre- 
cisely the same as that generated in the voltaic 
battery. 

The commutator may only collect the currents 
as they are generated, and supply what is called 
an alternating current, that is to say, a current 
which alternates or changes its direction several 
hundred times a second, or it may sift the cur- 
rents as they are produced and supply what is 
termed a continuous current, that is, a current 
always in the same direction, like that of a 
voltaic battery. Some machines are made to 
supply alternating currents, others continuous 
currents. Either class of current will do for 
electric lamps, but only continuous currents are 
used for electo-plating, or, in general, for electric 
motors. 

In the ** magneto-electric " machine \\\^ field 
magnets are simply steel bars permanently mag- 
netised, but in the ordinary dynamo the field 
magnets are electro-magnets excited to a high 



68 



THE STORY OF ELECTRICITY. 



pitch by means of the current generated in the 
moving conductor or armature. In the *^ series- 
wound " machine the whole of the current gener- 
ated in the armature also goes through the 
coils of the field magnets. Such a machine is 
sketched in figure 40, where A is the armature, 
consisting of an iron core surrounded by coils 
of wire and rotating m the field of a powerful 
electro-magnet NS in the direction of the arrows. 
For the sake of simplicity only twelve coils are 




Fig. 40. — A Dynamo. 

represented. They are all in circuit one with 
another, and a wire connects the ends of each 
coil to corresponding metal bars on the commu- 
tator c. These bars are insulated from each other 
on the spindle X of the armature. Now, as each 
coil passes through the magnetic field in turn, 
a current is excited in it. Each coil therefore 
resembles an individual cell of a voltaic battery, 
connected in series. The current is drawn off 
from the ring by two copper '' brushes " ^, b\ 



THE ELECTRICITY OF MAGNETISM. 69 

which rub upon the bars of the commutator at 
opposite ends of a diameter, as shown. One 
brush is the positive pole of the dynamo, the 
other is the negative, and the current will flow 
through any wire or external circuit which may 
be connected with these, whether electric lamps, 
motors, accumulators, electro-plating baths, or 
other device. The small arrows show the move- 
ments of the current throughout the machine, 
and the terminals are marked ( + ) positive and 
( — ) negative. 

It will be observed that the current excited in 
the armature also flows through the coils of the 
electro-magnets, and thus keeps up their strength. 
When the machine is first started the current is 
feeble, because the field of the magnets in w^hich 
the armature revolves is merely that due to the 
dregs or " residual magnetism " left in the soft 
iron cores of the magnet since the last time the 
machine was used. But this feeble current exalts 
the strength of the field-magnets, producing a 
stronger field, which in turn excites a still 
stronger current in the armature, and this pro- 
cess of give and take goes on until the full 
strength or '^saturation" of the magnets is at- 
tained. 

Such is the "series" dynamo, of which the 
well-known Gramme machine is a type. Figure 
41 illustrates this machine as it is actually made, 
A being the armature revolving between the 
poles N S of the field-magnets MM, M' M\ on a 
spindle which is driven by means of a belt on 
the pulley F from a separate engine. The brushes 
b b' of the commutator C collect the current, 
which in this case is continuous, or constant in 
its direction. 



70 



THE STORY OF ELECTRICITY. 



The current of the series machine varies with 
the resistance of the external or working circuit, 
because that is included in the circuit of the field 
magnets and the armature. Thus, if we vary the 
number of electric lamps fed by the machine, we 
shall vary the current it is capable of yielding. 
With arc lamps in series, by adding to the number 
in circuit we increase the resistance of the outer 




Fig. 41. 

circuit, and therefore diminish the strength of 
the current yielded by the machine, because the 
current, weakened by the increase of resistance, 
fails to excite the field magnets as strongly as 
before. On the other hand, with glow lamps 
arranged in parallel, the reverse is the case, and 
putting more lamps in circuit increases the power 



THE ELECTRICITY OF MAGNETISM. 



71 



M 

nnnnnnr\ 



f 




of the machine, by diminishing the resistance of 
the outer circuit in providing more cross-cuts for 
the current. This, of course, is a drawback to the 
series machine in places where the number of 
lamps to be Hghted varies from time to time. 
In the "shunt-wound " machine the field magnets 
are excited by diverting a small portion of the 
main current from the armature through them, 
by means of a " shunt " or loop circuit. Thus in 
figure 42 where C is the 
commutator and /^ b' the 
brushes, J/ is a shunt 
circuit through the mag- 
nets, and E is the exter- 
nal or working circuit of 
the machine. 

The small arrows in- 
dicate the directions of 
the currents. With this 
arrangement the addition 
of more glow lamps to 
the external circuit E di- 
minishes the current, be- 
cause the portion of it which flows through the 
by-path J/, and excites the magnets, is less now 
that the alternative route for the current through 
E is of lower resistance than before. When fewer 
glow lamps are in the external circuit E, and its 
resistance therefore higher, the current in the shunt 
circuit M is greater than before, the magnets be- 
come stronger, and the electromotive force of the 
armature is increased. The Edison machine is of 
this type, and is illustrated in figure 43, where 
MM' are the field magnets with their poles A^ S, 
between which the armature A is revolved by 
means of the belt B, and a pulley seen behind. 



h 



lA/VAy\A/VV 
E 

Fig. 42. 



72 



THE STORY OF ELECTRICITY. 



The leading wires W W convey the current from 
the brushes of the commutator to the external 




Fig. 43. 

circuit. In this machine the conductors of the 
armature are not coils of wire, but separate bars 
of copper. 

In shunt machines the variation of current due 



THE ELECTRICITY OF MAGNETISM. 73 

to a varying number of lamps in use occasions a 
rise and fall in the brightness of the lamps which 
is undesirable, and hence a third class of dynamo 
has been devised, which combines the principles 
of both the series and shunt machines. This is 
the "compound-wound" machine, in which the 
magnets are wound partly in shunt and partly in 
series with the armature, in such a manner that 
the strength of the field-magnets and the electro- 
motive force of the current do not vary much, 
whatever be the number of lamps in circuit. In 
alternate current machines the electromotive force 
keeps constant, as the field-magnets are excited 
by a separate machine, giving a continuous cur- 
rent. 

We have already seen that the action of the 
dynamo is reversible, and that just as a wire 
moved across a magnetic field supplies an electric 
current, so a wire at rest, but conducting a cur- 
rent across a magnetic field, will move. The 
electric motor is therefore essentially a dynamo, 
which on being traversed by an electric current 
from an external source puts itself in motion. 
Thus, if a current be sent through the armature 
of the Gramme machine, shown in figure 41, the 
armature will revolve, and the spindle, by means 
of a belt on the pulley jP, can communicate its 
energy to another machine. 

Hence the electric motor can be employed to 
work lathes, hoists, lifts, drive the screws of boats 
or the wheels of carriages, and for many other 
purposes. There are numerous types of electric 
motor as of the dynamo in use, but they are all 
modifications of the simple continuous or alter- 
nating current dynamo. 

Obviously, since mechanical power can be 



74 THE STORY OF ELECTRICITY. 

converted into electricity by the dynamo, and re- 
converted into mechanical power by the motor, it 
is sufficient to connect a dynamo and motor to- 
gether by insulated wire in order to transmit me- 
chanical power, whether it be derived from wind, 
water, or fuel, to any reasonable distance. 



CHAPTER V. 

ELECTROLYSIS. 

Having seen how electricity can be generated 
and stored in considerable quantity, let us now 
turn to its practical uses. Of these by far the 
most important are based on its property of de- 
veloping light and heat as in the electric spark, 
chemical action as in the voltameter, and magnet- 
ism as in the electromagnet. 

The words "current," "pressure," and so on 
point to a certain analogy between electricity and 
water, which helps the imagination to figure what 
can neither be seen nor handled, though it must 
not be traced too far. Water, for example, runs 
by the force of gravity from a place of higher to 
a place of lower level. The pressure of the 
stream is greater the more the difference of level 
or " head of water." The strength of the current 
or quantity of water flowing per second is greater 
the higher the pressure, and the less the resist- 
ance of its channel. The power of the water or 
its rate of doing mechanical work is greater the 
higher the pressure and the stronger the current. 

So, too, electricity flows by the electromotive 
force from a place of higher to a place of lower 



ELECTROLYSIS. 75 

electric level or potential. The electric pressure 
is greater the more the difference of potential or 
electromotive force. The strength of the electric 
current or quantity of electricity flowing per sec- 
ond is greater the higher the pressure or electro- 
motive force and the less the resistance of the 
circuit. The power of the electricity or its rate 
of doing work is greater the higher the electro- 
motive force and the stronger the current. 

It follows that a small quantity of water or 
electricity at a high pressure will give us the 
same amount of energy as a large quantity at a 
low pressure, and our choice of one or the other 
will depend on the purpose we have in view. As 
a rule, however, a large current at a compara- 
tively low or moderate pressure is found the more 
convenient in practice. 

The electricity of friction belongs to the 
former category, and the electricity of chemistry, 
heat, and magnetism to the latter. The spark of 
a frictional or influence machine can be compared 
to a highland cataract of lofty height but small 
volume, which is more picturesque than useful, 
and the current from a voltaic battery, a thermo- 
pile, or a dynamo to a lowland river which can 
be dammed to turn a mill. It is the difference 
between a skittish gelding and a tame cart- 
horse. 

Not the spark from an induction coil or Ley- 
den jar, but a strong and steady current at a low 
pressure, is adapted for electrolysis or electro-de- 
position, and hence the voltaic battery or a special 
form of dynamo is usually employed in this work. 
A flash of lightning is the very symbol of terrific 
power, and yet, according to the illustrious Fara- 
day, it contains a smaller amount of electricity 



76 THE STORY OF ELECTRICITY. 

than the feeble current required to decompose a 
single drop of rain. 

In our simile of the mill dam and the battery 
or dynamo, the dam corresponds to the positive 
pole and the river or sea below the mill to the 
negative pole. The mill-race will stand for the 
wire joining the poles, that is to say, the external 
circuit, and the mill-wheel for the work to be done 
in the circuit, whether it be a chemical for decom- 
position, a telegraph instrument, an electric lamp, 
or any other appliance. As the current in the 
race depends on the " head of water," or differ- 
ence of level between the dam and the sea as well 
as on the resistance of the channel, so the cur- 
rent in the circuit depends on the ** electromotive 
force," or difference of potential between the posi- 
tive and negative poles, as well as on the resist- 
ance of the circuit. The relation between these 
is expressed by the well-known law of Ohm, which 
runs : A current of electjHcity is directly propoi^tional 
to the electro7Jiotive force and inversely proportional 
to the resistance of the circuit. 

In practice electricity is measured by various 
units or standards named after celebrated elec- 
tricians. Thus the unit of quantity is the coulo7?ib, 
the unit of current or quantity flowing per second 
is the ampere, the unit of electromotive force is 
the volt^ and the unit of resistance is the o/mt. 

The quantity of water or any other "electro- 
lyte " decomposed by electricity is proportional 
to the strength of the current. One ampere de- 
composes .00009324 gramme of water per second, 
liberating .000010384 gramme of hydrogen and 
.00008286 gramme of oxygen. 

The quantity in grammes of any other chemi- 
cal element or ion which is liberated from an elec- 



ELECTROLYSIS. 77 

trolyte or body capable of electro-chemical de- 
composition in a second by a current of one 
ampere is given by what is called the electro- 
chemical equivalent of the ion. This is found by 
multiplying its ordinary chemical equivalent or 
combining weight by .000010384, which is the elec- 
tro-chemical equivalent of hydrogen. Thus the 
weight of metal deposited from a solution of any 
of its salts by a current of so many amperes in so 
many seconds is equal to the number of amperes 
multiplied by the number of seconds, and by the 
electro-chemical equivalent of the metal. 

The deposition of a metal from a solution of 
its salt is very easily shown in the case of cop- 
per. In fact, we have already seen that in the 
Daniell cell the current decomposes a solution of 
sulphate of copper and deposits the pure metal 
on the copper plate. If we simply make a solu- 
tion of blue vitriol in a glass beaker and dip the 
wires from a voltaic cell into it, we shall find the 
wire from the negative pole become freshly coated 
with particles of new copper. The sulphate has 
been broken up, and the liberated metal, being 
positive, gathers on the negative electrode. 
Moreover, if we examine the positive electrode 
we shall find it slightly eaten away, because the 
sulphuric acid set free from the sulphate has 
combined with the particles of that wire to make 
new sulphate. Thus the copper is deposited on 
one electrode, namely, the cathode, by which the 
current leaves the bath, and at the expense of 
the other electrode, that is to say, the anode, by 
which the current enters the bath. 

The fact that the weight of metal deposited in 
this way from its salts is proportional to the 
current, has been utilised for measuring the 



78 



THE STORY OF ELECTRICITY. 



strength of currents with a fine degree of ac- 
curacy. If, for example, the tubes of the vol- 
tameter described on page ;^S were graduated, 
the volume of gas evolved would be a measure 
of the current. Usually, however, it is the 
weight of silver or copper deposited from their 
salts in a certain time w^hich gives the current in 
amperes. 

Electro-plating is the principal application of 
this chemical process. In 1805 Brugnatelli took 
a silver medal and coated it with gold by making 
it the cathode in a solution of a salt of gold, and 
using a plate of gold for the anode. The shops 
of our jewellers are now bright with teapots, salt 
cellars, spoons, and other articles of the table 
made of inferior metals, but beautified and pre- 
served from rust in this way. 

Figure 44 illustrates an electro-plating bath 




Fig. 44. 

in which a number of spoons are being plated. 
A portion of the vat V is cut away to show the 
interior, which contains a solution S of the double 
cyanide of gold and potassium when gold is to be 



ELECTROLYSIS. 



79 



laid, and the double cyanide of silver and potas- 
sium when silver is to be deposited. The elec- 
trodes are hung from metal rods, the anode A 
being a plate of gold or silver G, as the case may 
be, and the cathode C the spoons in question. 
When the current of the battery or dynamo 
passes through the bath from the anode to the 
cathode, gold or silver is deposited on the spoons, 
and the bath recuperates its strength by consum- 
ing the gold or silver plate. 

Enormous quantities of copper are now de- 
posited in a similar way, sulphate of copper being 
the solution and a copper plate the anode. Large 
articles of iron, such as the parts of ordnance, are 
sometimes copper-plated to preserve them from 
the action of the atmosphere. Seamless copper 
pipes for conveying steam, and wires of pure cop- 
per for conducting electricity, are also deposited, 
and it is not unlikely that the kettle of the future 
will be made by electrolysis. 

Nickel-plating is another extensive branch of 
the industry, the white nickel forming a cloak 
for metals more subject to corrosion. Nickel is 
found to deposit best from a solution of the 
double sulphate of nickel and ammonia. Alu- 
minium, however, has not yet been successfully 
deposited by electricity. 

In 1836 De la Rue observed that copper laid 
in this manner on another surface took on its 
under side an accurate impression of that surface, 
even to the scratches on it, and three years later 
Jacobi, of St. Petersburg, and Jordan, of London, 
applied the method to making copies or replicas 
of medals and woodcuts. Even non-metallic sur- 
faces could be reproduced in copper by taking a 
cast of them in wax and lining the mould with 



8o THE STORY OF ELECTRICITY. 

fine plumbago, which, being a conductor, served 
as a cathode to receive the layer of metal. It is 
by the process of electrotyping or galvano-plastics 
that the copper faces for printing woodcuts are 
prepared, and copies made of seals or medals. 

Natural objects, such as flowers, ferns, leaves, 
feathers, insects, and lizards, can be prettily 
coated with bronze or copper, not to speak of 
gold and silver, by a similar process. They are 
too delicate to be coated with black lead in order 
to receive the skin of metal, but they can be 
dipped in solutions, leaving a film which can be 
reduced to gold or silver. For instance, they may 
be soaked in an alcoholic solution of nitrate of 
silver, made by shaking 2 parts of the crystals in 
100 parts of alcohol in a stoppered bottle. When 
dry, the object should be suspended under a glass 
shade and exposed to a stream of sulphuretted 
hydrogen gas ; or it may be immersed in a solu- 
tion of I part of phosphorus in 15 parts of bisul- 
phide of carbon, i part of bees-wax, i part of 
spirits of turpentine, i part of asphaltum, and '/g 
part of caoutchouc dissolved in bisulphide of car- 
bon. This leaves a superficial film which is 
metallised by dipping in a solution of 20 grains 
of nitrate of silver to a pint of water. On this 
metallic film a thicker layer of gold and silver in 
different shades can be deposited by the current, 
and the silver surface may also be ** oxidised " 
by washing it in a weak solution of platinum 
chloride. 

Electrolysis is also used to some extent in 
reducing metals from their ores, in bleaching 
fibre, in manufacturing hydrogen and oxygen 
from water, and in the chemical treatment of 
sewage. 



THE TELEGRAPH AND TELEPHONE. Si 

CHAPTER VI. 

THE TELEGRAPH AND TELEPHONE. 

Like the *^ philosopher's stone," the *' elixir of 
youth," and *' perpetual motion," the telegraph 
was long a dream of the imagination. In the 
sixteenth century, if not before, it was believed 
that two magnetic needles could be made sym- 
pathetic, so that when one was moved the other 
would likewise move, however far apart they 
were, and thus enable two distant friends to com- 
municate their minds to one another. 

The idea was prophetic, although the means 
of giving effect to it were mistaken. It became 
practicable, however, when Oersted discovered 
tnat a magnetic needle could be swung to one 
side or the other by an electric current passing 
near it. 

The illustrious Laplace was the first to suggest 
a telegraph on this principle. A wire connecting 
the two poles of a battery is traversed, as we 
know, by an electric current, which makes the 
round of the circuit, and only flows when that 
circuit is complete. However long the wire may 
be, however far it may run between the poles, 
the current will follow all its windings, and finish 
its course from pole to pole of the battery. You 
may lead the wire across the ocean and back, or 
round the world if you will, and the current will 
travel through it. 

The moment you break the wire or circuit, 
however, the current will stop. By its electro- 
motive force it can overcome the resistance of 
the many miles of conductor ; but unless it be 
6 



82 THE STORY OF ELECTRICITY. 

unusually strong it cannot leap across even a 
minute gap of air, which is one of the best in- 
sulators. 

If, then, we have a simple device easily manip- 
ulated by which we can interrupt the circuit of 
the battery, in accordance with a given code, we 
shall be able to send a series of currents through 
the wire and make sensible signals wherever we 
choose. These signs can be produced by the 
deviation of a magnetic needle, as Laplace pointed 
out, or by causing an electro-magnet to attract 
soft iron, or by chemical decomposition, or any 
other sensible effect of the current. 

Ampere developed the idea of Laplace into a 
definite plan, and in 1830 or thereabout Ritchie, 
in London, and Baron Schilling, in St. Petersburg, 
exhibited experimental models. In 1833 and 
afterwards Professors Gauss and Weber installed 
a private telegraph between the observatory and 
the physical cabinet of the University of Got- 
tingen. Moreover, in 1836 William Fothergill 
Cooke, a retired surgeon of the Madras army, 
attending lectures on anatomy at the University 
of Heidelberg, saw an experimental telegraph of 
Professor Moncke, which turned all his thoughts 
to the subject. On returning to London he made 
the acquaintance of Professor Wheatstone, of 
King's College, who was also experimenting in 
this direction, and in 1836 they took out a 
patent for a needle telegraph. It w^as tried 
successfully between the Euston terminus and 
the Camden Town station of the London and 
North-Western Railway on the evening of July 
25th, 1837, in presence of Mr. Robert Stephen- 
son, and other eminent engineers. Wheatstone, 
sitting in a small room near the booking-office at 



THE TELEGRAPH AND TELEPHONE. S3 

Euston, sent the first message to Cooke at Cam- 
den Town, who at once repHed. " Never," said 
Wheatstone, "did I feel such a tumultuous sensa- 
tion before, as when, all alone in the still room, I 
heard the needles click, and as I spelled the 
words I felt all the magnitude of the invention 
pronounced to be practicable without cavil or 
dispute." 

The importance of the telegraph in working 
railways was manifest, and yet the directors of 
the company were so purblind as to order the 
removal of the apparatus, and it was not until 
two years later that the Great Western Railway 
Company adopted it on their line from Padding- 
ton to West Drayton, and subsequently to Slough. 
This was the first telegraph for public use, not 
merely in England, but the world. The charge 
for a message was only a shilling, nevertheless 
few persons availed themselves of the new inven- 
tion, and it was not until its fame was spread 
abroad by the clever capture of a murderer 
named Tawell that it began to prosper. Tawell 
had killed a woman at Slough, and on leaving his 
victim took the train for Paddington. The police, 
apprised of the murder, telegraphed a description 
of him to London. The original "five needle 
instrument," now in the museum of the Post 
Ofiice, had a dial in the shape of a diamond, on 
which were marked the letters of the alphabet, 
and each letter of a word was pointed out by the 
movements of a pair of needles. The dial had 
no letter " q," and as the man was described as 
a quaker the word was sent " kwaker." When 
the train arrived at Paddington he was shadowed 
by detectives, and to his utter astonishment was 
quietly arrested in a tavern near Cannon Street. 



84 



THE STORY OF ELECTRICITY. 



In Cooke and Wheatstone's early telegraph 
the wire travelled the whole round of the circuit, 
but it was soon found that a " return " wire in 
the circuit was unnecessary, since the earth itself 
could take the place of it. One wire from the 
sending station to the receiving station was 
sufficient, provided the apparatus at each end 
were properly connected to the ground. This 
use of the earth not only saved the expense of a 
return wire, but diminished the resistance of the 
circuit, because the earth offered practically no 
resistance. 

Figure 45 is a diagram of the connections in a 









m//////mi 




R Ct 



Fig. 45. 

simple telegraph circuit. At each of the stations 
there is a battery B B\ an interrupter or sending 
key K K' to make and break the continuity of the 
circuit, a receiving instrument R R' to indicate 
the signal currents by their sensible effects, and 
connections with ground or " earth plates " E E' 
to engage the earth as a return wire. These 
are usually copper plates buried in the moist 
subsoil or the water pipes of a city. The line 
wire is commonly of iron supported on poles, 
but insulated from them by earthenware "cups" 
or insulators. 

At the station on the left the key is in the act 



THE TELEGRAPH AND TELEPHONE. 85 

of st'/ii/i/{i^^ a message, and at the post on the right 
it is conformably in the position for receiving the 
message. The key is so constructed that when it 
IS at rest it puts the line in connection with the 
earth through the receiving instrunient and the 
earth plate. 

The key K consists essentially of a spring- 
lever, with two platinum contacts, so placed that 
when the lever is pressed down by the hand of 
the telegraphist it breaks contact with the re- 
ceiver R, and puts the line-wire L in connection 
with the earth ^through the battery B, as shown 
on the left. A current then flows into the line 
and traverses the receiver R' at the distant sta- 
tion, returning or seeming to return to the send- 
ing battery by way of the earth plate E' on the 
right and the intermediate ground. 

The duration of the current is at the will of 
the operator who works the sending-key, and it is 
plain that signals can be made by currents of 
various lengths. In the " Morse code " of sig- 
nals, which is now universal, only two lengths of 
current are employed — namely, a short, momen- 
tary pulse, produced by instant contact of the 
key, and a jet given by a contact about three 
times longer. These two signals are called 
" dot " and '' dash," and the code is merely a suit- 
able combination of them to signify the several 
letters of the alphabet. Thus e^ the commonest 
letter in English, is telegraphed by a single *' dot," 
and the letter / by a single *'dash," while the let- 
ter a is indicated by a '' dot " followed after a brief 
interval or '' space " by a dash. 

Obviously, if two kinds of current are used, 
that is to say, if the poles of the battery are 
reversed by the sending-key, and the direction 



86 THE STORY OF ELECTRICITY. 

of the current is consequently reversed in the 
circuit, there is no need to alter the length of the 
signal currents, because a momentary current 
sent in one direction will stand for a ^^ dot ** and 
in the other direction for a ^' dash." As a matter . 
of fact, the code is used in both ways, according 
to the nature of the line and receiving instru- 
ment. On submarine cables and with needle 
and '^ mirror " instruments, the signals are made 
by reversing currents of equal duration, but on 
land lines worked by *^ Morse " instruments and 
** sounders," they are produced by short and long 
currents. 

The Morse code is also used in the army for 
signalling by waving flags or flashing lights, and 
may also be serviceable in private life. Tele- 
graph clerks have been known to " speak " with 
each other in company by winking the right 
and left eye, or tapping with their teaspoon on 
a cup and saucer. Any two distinct signs, how- 
ever made, can be employed as a telegraph by 
means of the Morse code, which runs as shown 
in figure 46. 

The receiving instruments J^ J^^ may consist 
of a magnetic needle pivotted on its centre and 
surrounded by a coil of wire, through which the 
current passes and deflects the needle to one side 
or the other, according to the direction in which 
it flows. Such was the pioneer instrument of 
Cooke and Wheatstone, which is still employed 
in England in a simplified form as the " single " 
and ^^ double " needle-instrument on some of the 
local lines and in railway telegraphs. The signals 
are made by sending momentary currents in oppo- 
site directions by a " double current " key, which 
(unlike the key X in figure 45) reverses the poles 



THE TELEGRAPH AND TELEPHONE. 



87 



Needle and 




Needle and 


Morse Instrument. Mirror 


Morse Instrument. 


Mirror 


Ins 


trument 




Instrument 


A ._ 


x/ 


J 


K/// 


ti(ap) 


yy 


K 


yy 


B 


/.x. 


L 


ty.s 


c 


A/- 


M 


y/ 


D 


/sS 


X _ . 


/. 


E 


\ 





/// 


F 


/ 




///. 


6 


//. 


p 


y/x 


H 


WW 


Q 


//y 


I 


\\ 


R 


.A 


9 -.- 


/ 


1 


y/// 


T ^ 


__ ^^ ___ 


../// 


U . 




ssJ/ 


u (ue) , 


vv// 


! 4 


..y 


V 


vxv/ 








y/ 

A/ 


5 


\\\\\ 


w 


G 


/\\\\ 


X 




/Avx 


\ 


A// 


8 - 


///. 


Z 


//. 




////. 


Ch 


//// 





/////■ 



P^iu. 46. — Morse Signal Alphabet. 

of the battery, in putting the hne to one or the 
other, and thus making the ^' dot '' signal with 
the " positive " and the '^ dash " signal with the 
negative pole. It follows that if the ^' dot " is 
indicated by a throw of the needle to the right 
side, a "dash" will be given by a throw to the 
left. 

Most of the telegraph instruments for land 
lines are based on the principle of the electro- 



THE STORY OF ELECTRICITY. 



magnet. We have already seen (page 59) how 
Ampere found that a spiral of wire with a cur- 
rent flowing in it behaved like a magnet and was 
able to suck a piece of soft iron into it. If the 
iron is allowed to remain there as a core, the 
combination of coil and core becomes an electro- 
magnet, that is to say, a magnet which is only a 
magnet so long as the current passes. Figure 
47 represents a simple '' horse-shoe " electro- 
^ magnet as invented by 

Sturgeon. A U-shaped 
core of soft iron is 
wound with insulated 
wire W, and when a 
current is sent through 
the wire, the core is 
found to become mag- 
netic with a " north " 
pole in one end and a 
''south" pole in the 
other. These poles 
are therefore able to 
attract a separate piece 
of soft iron or armature A. When the cur- 
rent is stopped, however, the core ceases to be 
a magnet and the armature drops away. In prac- 
tice the electromagnet usually takes the form 
shown in figure 48, where the poles are two bob- 
bins or solenoids of wire S having straight cores 
of iron which are united by an iron bar^, and A 
is the armature. 

Such an electromagnet is a more powerful 
device than a swinging needle, and better able to 
actuate a mechanism. It became the foundation 
of the recording instrument of Samuel Morse, the 
father of the telegraph in America. The Morse, 




Fig. 47. 
A Simple Electro Magnet. 



THE TELEGRAPH AND TELEPHONE. 



89 



or, rather, Morse and Vail instrument, actually 
marks the signals in ** dots " and " dashes " on a 
ribbon of moving paper. Figure 49 represents 
the Morse instrument, in which an electromagnet 
M attracts an iron armature A when a current 
passes through its bobbins, and by means of a 
lever L connected with the armature raises the 
edge of a small disc out 
of an ink-pot / against 
the surface of a travelling 
slip of paper F, and marks 
a dot or dash upon it as 
the case may be. The 
rest of the apparatus con- 
sists of details and ac- 
cessories for its action 
and adjustment, together 
with the sending-key K, which is used in asking 
for repetitions of the words, if necessary. 

A permanent record of the message is of 




Fig. 48.— Electro Ma^et. 




Fig. 49. 



course convenient, nevertheless the operators 
prefer to '* read " the signals by the ear, rather 
than the eye, and, to the annoyance of Morse, 



90 



THE STORY OF ELECTRICITY. 



would listen to the click of the marking disc 
rather than decipher the marks on the paper. 
Consequently Stephen Vail, the collaborator of 
Morse, who really invented the Morse code, pro- 
duced a modification of the recording instrument 
working solely for the ear. The '' sounder," as 
it is called, has largely driven the " printer ** 
from the field. This neat little instrument is 
shown in figure 50, where M is the electromag- 
net, and A is the armature which chatters up and 




Fig. 50. 

down between two metal stops, as the current is 
made and broken by the sending-key, and the 
operator listening to the sounds interprets the 
message letter by letter and word by word. 

The motion of the armature in both of these 
instruments takes a sensible time, but Alexander 
Bain, of Thurso, by trade a watchmaker, and by 
nature a genius, invented a chemical telegraph 
which was capable of a prodigious activity. The 
instrument of Bain resembled the Morse in mark- 
ing the signals on a tape of moving paper, but 



THt: TELEGRAPH AXD TELEPHONE. 91 

this was done by electrolysis or electro-chemical 
decomposition. The paper was soaked in a solu- 
tion of iodide of potassium in starch and water, 
and the signal currents were passed through it 
by a marking stylus or pencil of iron. The elec- 
tricity decomposed the solution in its passage and 
left a blue stain on the paper, which corresponded 
to the dot and dash of the Morse apparatus. 
The Bain telegraph can record over 1000 words 
a minute as against 40 to 50 by the Morse or 
sounder, nevertheless it has fallen into disuse, 
perhaps because the solution was troublesome. 

It is stated that a certain blind operator could 
read the. signals by the smell of the chemical ac- 
tion ; and we can well believe it. In fact, the 
telegraph appeals to every sense, for a deaf clerk 
can feel the movements of a sounder, and the 
signals of the current can be told without any 
instrument by the mere taste of the wires inserted 
in the mouth. 

A skilful telegraphist can transmit twenty-five 
words a minute with the single-current key, and 
nearly twice as many by the double-current key, 
and if we remember that an average English 
word requires fifteen separate signals, the num- 
ber will seem remarkable ; but by means of 
Wheatstone's automatic sender 150 words or 
more can be sent in a minute. 

Among telegraphs designed to print the mes- 
sage in Roman type, that of Professor David 
Edward Hughes is doubtless the fittest, since it 
is now in general use on the Continent, and con- 
veys our Continental news. In this apparatus 
the electromagnet, on attracting its armature, 
presses the paper against a revolving type wheel 
and receives the print of a type, so that the mes- 



92 THE STORY OF ELECTRICITY. 

sage can be read by a novice. To this effect the 
type wheel at the receiving station has to keep in 
perfect time as it revolves, so that the right letter 
shall be above the paper when the current passes. 
Small varieties of the type-printer are employed 
for the distribution of news and prices in most of 
the large towns, being located in hotels, restau- 
rants, saloons, and other public places, and re- 
porting prices of stocks and bonds, horse races, 
and sporting and general news. The ^' duplex 
system," whereby two messages, one in either 
direction, can be sent over one wire simultane- 
ously without interfering, and the quadruplex 
system, whereby four messages, two in either 
direction, are also sent at once, have come into 
use where the traffic over the lines is very great. 
Both of these systems and their modifications 
depend on an ingenious arrangement of the ap- 
paratus at each end of the line, by which the 
signal currents sent out from one station do not 
influence the receivers there, but leave them free 
to indicate the currents from the distant station. 
When the Wheatstone Automatic Sender is em- 
ployed with these systems about 500 words per 
minute can be sent through the line. Press news 
is generally sent by night, and it is on record, 
that during a great debate in Parliament, as many 
as half a million words poured out of the Central 
Telegraph Station at St. Martin's-le-Grand in a 
single night to all parts of the country. 

Errors occur now and then through bad pen- 
manship or the similarity of certain signals, and 
amusing telegrams have been sent out, as w^hen 
the nomination of Mr. Brand for the Speakership 
of the Commons took the form of ** Proposed to 
brand Speaker " ; and an excursion party assured 



THE TELEGRAPH AND TELEPHONE. 93 

their friends at home of their security by the 
message, "Arrived all tight." 

Telegraphs, in the literal sense of the word, 
which actually write the message as with a pen, 
and make a copy or facsimile of the original, 
have been invented from time to time. Such are 
the '^ telegraphic pen " of Mr. E. A. Cowper, and 
the ''telautographs" of Mr. J. H. Robertson and 
Mr. Elisha Gray. The first two are based on a 
method of varying the strength of the current 
in accordance with the curves of the handwriting, 
and making the varied current actuate by means 
of magnetism a writing pen or stylus at the 
distant station. The instrument of Gray, which 
is the most successful, works by intermittent 
currents or electrical impulses, that excite 
electro-magnets and move the stylus at the far 
end of the line. They are too complicated for 
description here, and are not of much practical 
importance. 

Telegraphs for transmitting sketches and draw- 
ings have also been devised by D'Ablincourt and 
others, but they have not come into general use. 
Of late another step forward has been taken by 
Mr. Amstutz, who has invented an apparatus for 
transmitting photographic pictures to a distance 
by means of electricity. The system may be 
described as a combination of the photograph 
and telegraph. An ordinary negative picture is 
taken, and then impressed on a gelatine plate 
sensitised with bichromate of potash. The parts 
of the gelatine in light become insoluble, while 
the parts in shade can be washed away by water. 
In this way a relief or engraving of the picture 
is obtained on the gelatine, and a cross section 
through the plate would, if looked at edgeways, 



94 THE STORY OF ELECTRICITY. 

appear serrated, or up and down, like a section 
of country or the trace of the stylus in the record 
of a phonograph. The gelatine plate thus carved 
by the action of light and water is wrapped round 
a revolving drum or barrel, and a spring stylus or 
point is caused to pass over it as the barrel re- 
volves, after the manner of a phonographic cylin- 
der. In doing so the stylus rises and falls over 
the projections in the plate and works a lever 
against a set of telegraph keys, which open elec- 
tric contacts and break the connections of an 
electric battery which is joined between the keys 
and the earth. There are four keys, and when 
they are untouched the current splits up through 
four by-paths or bobbins of wire before it enters 
the line wire and passes to the distant station. 
When any of the keys are touched, however, the 
corresponding by-path or bobbin is cut out of 
circuit. The suppression of a by-path or channel 
for the current has the effect of adding to the " re- 
sistance '* of the line, and therefore of diminishing 
the strength of the current. When all the keys 
are untouched the resistance is least and the cur- 
rent strongest. On the other hand, when all the 
keys but the last are touched, the resistance is 
greatest and the current weakest. By this device 
it is easy to see that as the stylus or tracer sinks 
into a hollow of the gelatine, or rises over a 
height, the current in the line becomes stronger 
or weaker. At the distant station the current 
passes through a solenoid or hollow coil of wire 
connected to the earth and magnetises it, so as 
to pull the soft iron plug or ^^ core " with greater 
or less force into its hollow interior. The up and 
down movement of the plug actuates a graving 
stylus or point through a lever, and engraves a 



THE TELEGRAPH AND TELEPHONE. 95 

copy of the original gelatine trace on the surface 
of a wax or gelatine plate overlying another 
barrel or drum, which revolves at a rate corre- 
sponding to that of the barrel at the transmitting 
station. In this way a facsimile of the gelatine 
picture is produced at the distant station, and an 
electrotype or cliche of it can be made for printing 
purposes. The method is, in fact, a species of 
electric line graving, and Mr. Amstutz hopes to 
apply it to engraving on gold, silver, or any soft 
metal, not necessarily at a distance. 

We know that an electric current in one wire 
can induce a transient current in a neighbouring 
wire, and the fact has been utilised in the United 
States by Phelps and others to send messages 
from moving trains. The signal currents are 
intermittent, and when they are passed through a 
conductor on the train they excite corresponding 
currents in a wire run along the track, which can 
be interpreted by the hum they make in a tele- 
phone. Experiments recently made by Mr. W. H. 
Preece for the Post Office show that with currents 
of sufficient strength and proper apparatus mes- 
sages can be sent through the air for five miles 
or more by this method of induction. 

We come now to the submarine telegraph, 
which differs in many respects from the overland 
telegraph. Obviously, since water and moist 
earth is a conductor, a wire to convey an electric 
current must be insulated if it is intended to lie 
at the bottom of the sea or buried underground. 
The best materials for the purpose yet discovered 
are gutta-percha and india-rubber, which are both 
flexible and very good insulators. 

The first submarine cable was laid across the 
Channel from Dover to Calais in 1851, ^nd con- 



96 



THE STORY OF ELECTRICITY. 



sisted of a copper strand, coated with gutta- 
percha, and protected from injury by an outer 
sheath of hemp and iron wire. It is the general 
type of all the submarine cables which have been 
deposited since then in every part of the world. 
As a rule, the armour or sheathing is made 
heavier for shore water than it is for the deep 
sea, but the electrical portion, or "core," that 




Irish Shore End. 
Fig. 51.— Section of the 1894 Atlantic Cable — Actual Size. 

is to say, the insulated conductor, is the same 
throughout. 

The first Atlantic cable was laid in 1858 by 
Cyrus W. Field and a company of British capital- 
ists, but it broke down, and it was not until 1866 
that a new and successful cable was laid to re- 



THE TELEGRAPH AND TELEPHONE. 



97 



place it. Figure 51 represents various cross- 
sections of an Atlantic cable deposited in 1894. 




Light Intermediate. 



Heavy Intermediate. 
Sections of the 1894 Atlantic Cable— Actual Sizes— 
continued. 

The inner star of twelve copper wires is the con- 
ductor, and the black circle round it is the gutta- 
7 



98 THE STORY OF ELECTRICITY. 

percha or insulator which keeps the electricity 
from escaping into the water. The core in shallow 
water is protected from the bites of teredoes by a 
brass tape, and the envelope or armour consists of 
hemp and iron wire preserved from corrosion by 
a covering of tape and a compound of mineral 
pitch and sand. 

The circuit of a submarine line is essentially 
the same as that of a land line, except that the 
earth connection is usually the iron sheathing of 
\the cable in lieu of an earth-plate. On a cable, 
however, at least a long cable, the instruments for 
sending and receiving the messages are different 
from those employed on a land line. A cable is 
virtually a Leyden jar or condenser, and the signal 
currents in the wire induce opposite currents in 
the water or earth. As these charges hold each 



^.- D 





Fig. 52. 

Other the signals are retarded in their progress, 
and altered from sharp sudden jets to lagging un- 
dulations or waves, which tend to run together or 
coalesce. The result is that the separate signal 
currents which enter a long cable issue from it at 
the other end in one continuous current, with pul- 
sations at every signal, that is to say, in a lapsing 
stream, like a jet of water flowing from a con- 
stricted spout. The receiving instrument must 



THE TELEGRAPH AND TELEPHONE. 99 

be sufficiently delicate to manifest every pulsation 
of the current. Its indicator, in fact, must re- 
spond to every rise and fall of the current, as a 
float rides on the ripples of a stream. 

Such an instrument is the beautiful '' mirror " 
i;alvanometer of Lord Kelvin, Ex-President of the 
Royal Society, which we illustrate in figure 52, 
where C is a coil of wire with a small magnetic 
needle suspended in its heart, and Z> is a steel 
magnet supported over it. The needle [Af figure 
53) is made of watch spring cemented to the back 
of a tiny mirror the size of a half-dime 
which is hung by a single fibre of floss 
silk inside an air cell or chamber with a 
glass lens G in front, and the coil C sur- 
rounds it. A ray of light from a lamp 
Z (figure 52) falls on the mirror, and is 
reflected back to a scale S, on which it 
makes a bright spot. Now, when the 
coil C is connected between the end of 
the cable and the earth, the signal current passing 
through it causes the tiny magnet to swing from 
side to side, and the mirror moving with it throws 
the beam up and down the scale. The operator 
sitting by watches the spot of light as it flits and 
flickers like a fire-fly in the darkness, and spells 
out the mysterious message. 

A condenser joined in the circuit between the 
cable and the receiver, or between the receiver 
and the earth, has the effect of sharpening the 
waves of the current, and consequently of the 
signals. The double-current key, which reverses 
the poles of the battery and allows the signal 
currents to be of one length, that is to say, all 
**dots," is employed to send the message. 

Another receiving instrument employed on 




lOO 



THE STORY OF ELECTRICITY. 



most of the longer cables is the 
siphon recorder of Lord Kelvin, 
shown in figure 54, which marks 
or writes the message on a slip 
of travelling paper. Essentially 
it is the inverse of the mir- 
ror instrument, and con- 
sists of a light coil of wire 
iS'suspended 
in the field 
between the 
poles of a 
strong mag- 
net J/. The 
coil is at- 
tached to 
a fine siphon (P) 
filled with ink, and 
sometimes kept in 
vibration by an in- 
duction coil so as 
to shake the ink 
in fine drops upon 
a slip of mov- 
ing paper. The 
coil is connected 
between the cable 
and the earth, and, 
as the signal 
current passes 

through, it swings 
to one side or the 
other, pulling the 
siphon with it. fig. 54. 

The ink, therefore, 
marks a wavy line on the paper, which is in fact a 




THE TELEGRAPH AND TELEPHONE. lOI 

delineation of the rise and fall of the signal current 
and a record of the message. The dots in this 
case are represented by the waves above, and the 
''dashes" by the waves below the middle line, as 
may be seen in the following alphabet, which is a 



/V 



Fig. 55. 

copy of one actually written by the recorder on a 
long submarine cable. 

Owing to induction, the speed of signalling on 
long cables is much slower than on land lines of 
the same length, and only reaches from 25 to 45 
words a minute on the Atlantic cables, or 30 to 
50 words with an automatic sending-key ; but this 
rate is practically doubled by employing the Muir- 
head duplex system of sending two messages, one 
from each end, at the same time. 

The relation of the telegraph to the telephone 
is analogous to that of the lower animals and 
man. In a telegraph circuit, with its clicking key 
at one end and its chattering sounder at the other, 
we have, in fact, an apish forerunner of the ex- 
quisite telephone, with its mysterious microphone 
and oracular plate. Nevertheless, the telephone 
descended from the telegraph in a very indirect 
manner, if at all, and certainly not through the 



102 



THE STORY OF ELECTRICITY. 



sounder. The first practical suggestion of an 
electric telephone was made by M. Charles Bour- 
seul, a French telegraphist, in 1854, but to all ap- 
pearance nothing came of it. In i860, however, 
Philipp Reis, a German schoolmaster, constructed 
a rudimentary telephone, by which music and a 
few spoken words were sent. Finally, in 1876, 
Mr. Alexander Graham Bell, a Scotchman, residing 
in Canada, and subsequently in the United States, 
exhibited a capable speaking telephone of his in- 
vention at the Centennial Exhibition, Philadel- 
phia. 

Figure 56 represents an outside view and sec- 
tion of the Bell telephone as it is now made, where 

J/ is a bar magnet having 
a small bobbin or coil of 
fine insulated wire C gir- 
dling one pole. In front 
of this coil there is a cir- 
cular plate of soft iron 
capable of vibrating like a 
M diaphragm or the drum of 
the ear. A cover shaped 
like a mouthpiece O fixes 
the diaphragm all round, 
and the wires IV W serve 
to connect the coil in the 
circuit. 

The soft iron diaphragm 
is, of course, magnetised 
Fig. 56. by the induction of the 

pole, and would be at- 
tracted bodily to the pole were it not fixed by 
the rim, so that only its middle is free to move. 
Now, when a person speaks into the mouthpiece 
the sonorous waves impinge on the diaphragm 



' Mil 

lu___JL ^ I ::i I 



THE TELEGRAPFI AND TELEPHONE. 103 

and make it vibrate in sympathy with them. Be- 
ing magnetic, the movement of the diaphragm 
to and from the bobbin excites corresponding- 
waves of electricity in the coil, after the famous 
experiment of Faraday (page 64). If this undula- 
tory current is passed through the coil of a similar 
telephone at the far end of the line, it will, by a 
reverse action, set the diaphragm in vibration and 
reproduce the original sonorous waves. The re- 
sult is, that when another person listens at the 
mouthpiece of the receiving telephone, he will 
hear a faithful imitation of the original speech. 

The Bell telephone is virtually a small mag- 
neto-electric generator of electricity, and when 
two are joined in circuit we have a system for the 
transmission of energy. As the voice is the mo- 
tive power, its talk, though distinct, is compara- 
tively feeble, and further improvements were 
made before the telephone became as serviceable 
as it is now. 

Edison, in 1877, was the first to invent a work- 
ing telephone, which, instead of generating the 
current, merely controlled the strength of it, as 
the sluice of a mill-dam regulates the flow of w^ater 
in the lead. Du Moncel had observed that powder 
of carbon altered in electrical resistance under 
pressure, and Edison found that lamp-black was so 
sensitive as to change in resistance under the im- 
pact of the sonorous waves. His transmitter con- 
sisted of a button or wafer of lamp-black behind 
a diaphragm, and connected in the circuit. On 
speaking to the diaphragm the sonorous waves 
pressed it against the button, and so varied the 
strength of the current in a sympathetic manner. 
The receiver of Edison was equally ingenious, 
and consisted of a cylinder of oreparerl chalk kept 



104 



THE STORY OF ELECTRICITY. 



in rotation and a brass stylus rubbing on it. 
When the undulatory current passed from the 
stylus to the chalk, the stylus slipped on the sur- 
face, and, being connected to a diaphragm, made 
it vibrate and repeat the original sounds. This 
^* electro-motograph " receiver was, however, 
given up, and a combination of the Edison trans- 
mitter and the Bell receiver came into use. 

At the end of 1877 Professor D. E. Hughes, a 
distinguished Welshman, inventor of the printing 
telegraph, discovered that any loose contact be- 
tween two conductors had the property of trans- 
mitting sounds by varying the strength of an 
electric current passing through it. Two pieces 
of metal — for instance, two nails or ends of wire 
— when brought into a loose or crazy contact 
under a slight pressure, and traversed by a cur- 
rent, will transmit speech. Two pieces of hard 
carbon are still better than metals, and if prop- 
erly adjusted will make the tread of a fly quite 
audible in a telephone connected with them. 
Such is the famous *^ mi- 
crophone," by which a .,-7<-7rr^nrtr?r-J 
faint sound can be — ^^y^^'^^ 
magnified to the [fh— X 

ear. V--rr>_ 

Figure 57 represents ^^^^^'^ 

what is known as the ^' pen- '^== 
cil " microphone, in which M 
is a pointed rod of hard car- 
bon, delicately poised be- 
tween two brackets of carbon, 
which are connected in cir- 
cuit with a battery B and a Bell telephone T. The 
joints of rod and bracket are so sensitive that the 
current flowing across them is affected in strength 



B^ 



^^UiLSJJ- 



Fig. 57. 



M 



THE TELEGRAPH AND TELEPHONE. 105 

by the slightest vibration, even the walking of an 
insect. If, therefore, we speak near this micro- 
phone, the sonorous waves, causing the pencil to 
vibrate, will so vary the current in accordance 
with them as to reproduce the sounds of the voice 
in the telephone. 

The true nature of the microphone is not yet 
known, but it is evident that the air or ether be- 
tween the surfaces in contact plays an important 
part in varying the resistance, and, therefore, 
the current. In fact, a small *' voltaic arc," not 
luminous, but dark, seems to be formed between 
the points, and the vibrations probably alter its 
length, and, consequently, its resistance. The 
fact that a microphone is reversible and can act 
as a receiver, though a poor one, tends to confirm 
this theory. Moreover, it is not unlikely that the 
slipping of the stylus in the electromotograph is 
due to a similar cause. Be this as it may, there 
can be no doubt that carbon powder and the 
lamp-black of the Edison button are essentially a 
cluster of microphones. 

Many varieties of the Hughes microphone un- 
der different names are now employed as transmit- 
ters in connection with the Bell telephone. Figure 
58 represents a simple micro-telephone circuit, 
where M is the Hughes microphone transmitter, 
T the Bell telephone receiver, B the battery, and 
£ E the earth-plates ; but sometimes a return 
wire is used in place of the '' earth." 

The line wire is usually of copper and its 
alloys, which are more suitable than iron, especi- 
ally for long distances. Just as the signal cur- 
rents in a submarine cable induce corresponding 
currents in the sea water which retard them, so 
the currents in a land wire induce corresponding 



io6 



THE STORY OF ELECTRICITY. 



currents in the earth, but in aerial Hnes the earth 
is generally so far away that the consequent re- 
tardation is negligible except in fast working on 
long lines. The Bell telephone, however, is ex- 
tremely sensitive, and this induction affects it so 




'^ 



Fig. 58. 



Qb 



much that a conversation through one wire can 
be overheard on a neighbouring wire. Moreover, 
there is such a thing as *^ self-induction " in a wire 
— that is to say, a current in a wire tends to in- 
duce an opposite current in the same wire, which 
is practically equivalent to. an increase of resist- 
ance in the wire. It is particularly observed at 
the starting and stopping of a current, and gives 
rise to what is called the " extra-spark " seen in 
breaking the circuit of an induction coil. It is 
also active in the vibratory currents of the tele- 
phone, and, like ordinary induction, tends to 
retard their passage. Copper being less suscep- 
tible of self-induction than iron, is preferred for 
trunk lines. The disturbing effect of ordinary 
induction is avoided by using a return wire or 
loop circuit, and crossing the going and coming 
wires so as to make them exchange places at 
intervals. Moreover, it is found that an indue- 



THE TELEGRAPH AND TELEPHONE. 107 

tion coil in the telephone circuit, like a condenser 
in the cable circuit, improves the working, and 
lience it is usual to join the battery and trans- 
mitter with the primary wire, and the secondary 
wire with the line and the receiver. 

The longest telephone line as yet made is that 
from New Vork to Chicago, a distance of 950 
miles. It is made of thick copper wire, erected 
on cedar poles 35 feet above the ground. 

Induction is so strong on submarine cables of 
50 or 100 miles in length that the delicate waves 
of the telephone current are smoothed away, and 
the speech is either muffled or entirely stifled. 
Nevertheless, a telephone cable 20 miles long 
was laid betw^een Dover and Calais in 1891, and 
another between Stranraer and Donaghadee more 
recently, thus placing Great Britain on speaking 
terms with France and other parts of the Con- 
tinent. 

Figure 59 shows a form of telephone appara- 
tus employed in the United Kingdom. In it the 
transmitter and receiver, together with a call-bell, 
which are required at each end of the line, are 
neatly combined. I'he transmitter is a Blake 
microphone, in which the loose joint is a contact 
of platinum on hard carbon. It is fitted up in- 
side the box, together with an induction coil, 
and J/ is the mouthpiece for speaking to it. The 
receiver is a pair of Bell telephones T T, which 
are detached from their hooks and held to the 
ear. A call-bell B serves to '' ring up " the cor- 
respondent at the other end of the line. 

Excepting private lines, the telephone is 
worked on the " exchange system " — that is to 
say, the wires running to different persons con- 
verge in a central exchange, where, by means of 



lo^ 



THE STORY OF ELECTRICITY. 



an apparatus called a " switch-board," they are 
connected together for the purpose of conversa- 
tion. 

A telephone exchange would make an excel- 




FiG. 59. 

lent subject for the artist. He delights to paint 
us a row of Venetian bead-stringers or a band of 
Sevillian cigarette-makers, but why does he shirk 
a bevy of industrious girls working a telephone 
exchange ? Let us peep into one of these retired 
haunts, where the modern Fates are cutting and 



THE TELEGRAPH AND TELEPHONE. 



109 



joining the lines of electric speech between man 
and man in a great city. 

The scene is a long, handsome room or gal- 
lery, with a singular piece of furniture in the 
shape of an L occupying the middle. This is the 
switchboard, in which the wires from the offices 
and homes of the subscribers are concentrated 
like the nerves in a ganglion. It is known as the 
" multiple switchboard," an American invention, 
and is divided into sections, over which the oper- 
ators preside. The lines of all the subscribers 
are brought to each section, so that the operator 
can cross-connect any two lines in the whole sys- 
tem without leaving her chair. Each section of 
the board is, in fact, an epitome of the whole, but 
it is physically impossible for a single operator to 
make all the connections of a large exchange, and 
the work is distributed amongst them. A multi- 
plicity of wires is therefore needed to connect, 
say, two thousand subscribers. These are all 
concealed, however, at the back of the board, 
and in charge of the electricians. The young 
lady operators have nothing to do with these, 
and so much the better for them, as it would 
puzzle their minds a good deal worse than a rav- 
elled skein of thread. Their duty is to sit in 
front of the board in comfortable seats at a long 
table and make the needful connections. The 
call-signal of a subscriber is given by the drop of 
a disc bearing his number. The operator then 
asks the subscriber by telephone what he wants, 
and on hearing the number of the other sub- 
scriber he wishes to speak with, she takes up a 
pair of brass plugs coupled by a flexible con- 
ductor and joins the lines of the subscribers on 
the switchboard by simply thrusting the plugs 



no THE STORY OF ELECTRICITY. 

into holes corresponding to the wires. The sub- 
scribers are then free to talk with each other 
undisturbed, and the end of the conversation is 
signalled to the operator. Every instant the call 
discs are dropping, the connecting plugs are 
thrust into the holes, and the girls are asking, 
^^ Hullo! hullo!" *'Are you there?" *^ Who are 
you ? " '' Have you finished ? " Yet all this con- 
stant activity goes on quietly, deftly — we might 
say elegantly — and in comparative silence, for the 
low tones of the girlish voices are soft and pleas- 
ing, and the harsher sounds of the subscriber are 
unheard in the room by all save the operator who 
attends to him. 



CHAPTER VII. 

ELECTRIC LIGHT AND HEAT. 

The electric spark was, of course, familiar to 
the early experimenters with electricity, but the 
electric light, as we know it, was first discovered 
by Sir Humphrey Davy, the Cornish philosopher, 
in the year 1811 or thereabout. With the magic 
of his ganius Davy transformed the spark into a 
brilliant glow by passing it between two points of 
carbon instead of metal. If, as in figure 60, we 
twist the wires (-f and — ) which come from a 
voltaic battery, say of 20 cells, about two carbon 
pencils, and bring their tips together in order to 
start the current, then draw them a little apart, 
we shall produce an artificial or mimic star. A 
sheet of dazzling light, which is called the elec- 
tric arc, is seen to bridge the gap. It is not a 



ELECTRIC LIGHT AND HEAT. 



I I I 




Fig. 6o. 



true flame, for there is little combustion, but 
rather a nebulous blaze of silvery lustre in a 
bluish veil of heated air. 
The points of carbon are 
white-hot, and the positive 
is eaten away into a hol- 
low or crater by the cur- 
rent, which violently tears 
its particles from their seat 
and whirls them into the 
fierce vortex of the arc. 
The negative remains 
pointed, but it is also worn 
away about half as fast as 
the positive. This wasting 

of the carbons tends to widen the arc too much 
and break the current, hence in arc lamps meant 
to yield the light for hours the sticks are made of 
a good length, and a self-acting mechanism feeds 
them forward to the arc as they are slowly con- 
sumed, thus maintaining the splendour of the 
illumination. 

Many ingenious lamps have been devised by 
Serrin, Dubosq, Siemens, Brockie, and others, 
some regulating the arc by clockwork and elec- 
tro-magnetism, or by thermal and other effects of 
the current. They are chiefly used for lighting 
halls and railway stations, streets and open spaces, 
search-lights and lighthouses. They are some- 
times naked, but as a rule their brightness is tem- 
pered by globes of ground or opal glass. In 
search-lights a parabolic mirror projects all the 
rays in any one direction, and in lighthouses the 
arc is placed in the focus of the condensing lenses, 
and the beam is visible for at least twenty or 
thirty miles on clear nights. Very powerful arc 



112 



THE STORY OF ELECTRICITY. 



lights, equivalent to hundreds of thousands of 
candles, can be seen for loo or 150 miles. 

Figure 61 illustrates the Pilsen lamp, in which 
the positive carbon G runs on rollers r r through 
the hollow interior of two solenoids or coils of 




Fig. 61. — The Pilsen Lamp 



wire MM' and carries at its middle a spindle- 
shaped piece of soft iron C. The current flows 
through the solenoid M on its way to the arc, but 
a branch or shunted portion of it flows through 
the solenoid M\ and as both of these solenoids 
act as electromagnets on the soft iron C, each 
tending to suck it into its interior, the iron rests 
between them when their powers are balanced. 
When, however, the arc grows too wide, and the 
current therefore becomes too weak, the shunt 
solenoid M' gains a purchase over the main sole- 
noid J/, and, pulling the iron core towards it, 
feeds the positive carbon to the arc. In this way 
the balance of the solenoids is readjusted, the 
current regains its normal strength, the arc its 
proper width, and the light its brilliancy. 

Figure 62 is a diagrammatic representation of 
the Brush arc lamp. X and Y are the line ter- 
minals connecting the lamp in circuit. On the 



ELECTRIC LIGHT AND HEAT. 



I I 



one hancl, the current splits and passes aroiiiul 
the hollow spools H H\ thence to the rod ^V 




Fig. 62. — The Brush Lamp. 



through the carbon A', the arc, the carbon K\ and 
thence through the lamp frame to Y. On the 
other hand, it runs in a resistance fine-wire coil 
around the magnet T, thence to Y. The opera- 
tion of the lamp is as follows : K and K'^ being 
in contact, a strong current starts through the 
lamp energising H and H\ which suck in their 
core pieces N and S, lifting 6', and by it the 
*' washer-clutch " IV and the rod JV and carbon A\ 
establishing the arc. A^is lifted until the increas- 
ing resistance of the lengthening arc weakens the 
current in H H^ and a balance is established. As 
the carbons burn away, C gradually lowers until 
a stop under /^ holds it horizontal and allows N 
to drop through W, and the lamp starts anew. If 
for any reason the resistance of the lamp becomes 
8 



114 THE STORY OF ELECTRICITY. 

too great, or the circuit is broken, the increased 
current through T draws up its armature, closing 
the contacts J/, thus short-circuiting the lamp 
through a thick, heavy wire coil on Z", which then 
keeps J/ closed, and prevents the dead lamp from 
interfering with the others on its line. Numer- 
ous modifications of this lamp are in very gen- 
eral use. 

Davy also found that a continuous wire or 
stick of carbon could be made white-hot by send- 
ing a sufficient current through it, and this fact is 
the basis of the incandescent lamp now so common 
in our homes. 

Wires of platinum, iridium, and other inoxi- 
disable metals raised to incandescence by the 
current are useful in firing mines, but they are 
not quite suitable for yielding a light, because at 
a very high temperature they begin to melt. 
Every solid body becomes red-hot — that is to say, 
emits rays of red light, at a temperature of about 
1000° Fahrenheit, yellow rays at 1300°, blue rays 
at 1500°, and white light at 2000°. It is found, 
however, that as the temperature of a wire is 
pushed beyond this figure the light emitted be- 
comes far more brilliant than the increase of 
temperature would seem to warrant. It there- 
fore pays to elevate the temperature of the fila- 
ment as high as possible. Unfortunately the 
most refractory metals, such as platinum and al- 
loys of platinum with iridium, fuse at a tempera- 
ture of about 3450° Fahrenheit. Electricians have 
therefore forsaken metals, and fallen back on 
carbon for producing a light. In 1845 ^^- Staite 
devised an incandescent lamp consisting of a fine 
rod or stick of carbon rendered white-hot by the 
current, and to preserve the carbon from burning 



ELECTRIC LICxHT AND HEAT. 



in the atmosphere, he enclosed it in a ghiss bulb, 
from which the air was exhausted by an air pumj\ 
Edison and Swan, in 1878, and subsequently, went 
a step further, and substituted a filament or fine 
thread of carbon for the rod. The new lamp 
united the advantages of wire in point of form 
with those of carbon as a material. The Edison 
filament was made by cutting thin slips of bam- 
boo and charring them, the Swan by carbonising 
linen fibre with sulphuric acid. It was subse- 
cjuently found that a hard skin could be given to 
the filament by '' flashing " it — that is to say, heat- 
ing it to incandescence by 
the current in an atmosphere 
of hydro - carbon gas. The 
filament thus treated becomes 
dense and resilient. 

Figure 63 represents an 
ordinary glow lamp of the 
Edison-Swan type, where £ 
is the filament, moulded into 
a loop, and cemented to two 
platinum wires or electrodes 
P penetrating the glass bulb 
B, which is exhausted of air. 

Platinum is chosen be- 
cause it expands and con- 
tracts with temperature about 
the same as glass, and hence 
there is little chance of the 
glass cracking through unequal stress. The vac- 
uum in the bulb is made by a mercurial air pump 
of the Sprengel sort, and the pressure of air in it 
is only about one-millionth of an atmosphere. 
The bulb is fastened with a holder like that 
shown in figure 64, where two little hooks // con- 




FlG. 63. 



ii6 



THE STORY OF ELECTRICITY. 




Fig. 64. 



nected to screw terminals T T are provided to 
make contact with the platinum terminals of the 
lamp (P, figure (y^), and the spiral 
spring, by pressing on the bulb, en- 
sures a good contact. 

Fig. 65 is a cut of the ordinary 
Edison lamp and socket. One end 
of the filament is connected to the 
metal screw ferule at the base. 
The other end is attached to the 
metal button in the centre of the 
extreme bottom of the base. 
Screwing the lamp 
into the socket au- 
tomatically connects the filament 
on one end to the screw, on the 
other to an insulated plate at the 
bottom of the socket. 

The resistance of such a fila- 
ment hot is about 200 ohms, and 
to produce a good light from it 
the battery or dynamo ought to 
give an electromotive force of at 
least 100 volts. Few voltaic 
cells or accumulators have an 
electromotive force of more than 
2 volts, therefore we require a 
battery of 50 cells joined in se- 
ries, each cell giving 2 volts, and 
the whole set 100 volts. The 
strength of current in the circuit 
must also be taken into account. 
To yield a good light such a 
lamp requires or ^^ takes " about 
\ an ampere. Hence the cells 
must be chosen with regard to fig. 65. 




ELECTRIC LIGHT AND HEAT. II7 

their size and internal resistance as well as to 
their kind, so that when the battery, in series, is 
connected to the lamp, the resistance of the luhole 
a>r///V, including the filament or lamp, the battery 
itself, and the connecting wires shall give by 
Ohm's law a current of \ an ampere. It will be un- 
derstood that the current has the same strength 
in every part of the circuit, no matter how it is 
made up. Thus, if ^ of an ampere is flowing in 
the lamp, it is also flowing in the battery and 
wires. An Edison-Swan lamp of this model gives 
a light of about 15 candles, and is well-adapted 
for illuminating the interior of houses. The tem- 
perature of the carbon filament is about 3450° 
Fahr. — that is to say, the temperature at which 
platinum melts. Similar lamps of various sizes 
and shapes are also made, some equivalent to as 
many as 100 candles, and fitted for large halls 
or streets, others emitting a tiny beam like the 
spark of a glow-worm, and designed for medical 
examinations, or lighting flowers, jewels, and 
dresses in theatres or ball-rooms. 

The electric incandescent lamp is pure and 
healthy, since it neither burns nor pollutes the 
air. It is also cool and safe, for it produces 
little heat, and cannot ignite any inflammable 
stuffs near it. Hence its peculiar merit as a 
light for colliers working in fiery mines. Inde- 
pendent of air, it acts equally well under water, 
and is therefore used by divers. Moreover, it 
can be fixed wherever a wire can be run, does 
not tarnish gilding, and lends itself to the most 
artistic decoration. 

Electric lamps are usually connected in circuit 
on the series, parallel, and three-wire system. 

The series system is shown in figure 66, where 



iiB 



THE STORY OF ELECTRICITY. 



the lamps L L follow each other in a row like 
beads on a string. It is commonly reserved for 



^M>-€>-G 



"^ 



-O 




Fig. 66. 

the arc lamp, which has a resistance so low that 
a moderate electromotive force can overcome the 
added resistance of the lamps, but, of course, if 



^ 




9 



^.t 



T 



1!> 



€ < r cc 
Fig. 67. 

the circuit breaks at any point all the lamps go 
out. 

The parallel system is illustrated in figure 67, 
where the lamps are connected between two main 
conductors cross-wise, like the steps of a ladder. 
The current is thus divided into cross channels, 
like water used for irrigating fields, and it is ob- 
vious that, although the circuit is broken at one 
point, say by the rupture of a filament, all the 
lamps do not go out. 



ELECTRIC LIGHT AND HEAT. 



119 



Fig. 68 exhibits the Edison three-wire system, 
in which two batteries or dynamos are connected 




Fig. 68. 



together in series, and a third or central main 
conductor is run from their middle poles. The plan 
saves a return wire, for if two generators had 
been used separately, four mains would have been 
necessary. 

The parallel and three-wire systems in various 
groups, with or without accumulators as local 
reservoirs, are chiefly employed for incandescent 
lamps. 

The main conductors conveying the current 
from the dynamos are commonly of stout copper 
insulated with air like telegraph wires, or cables 
coated with india-rubber or gutta-percha, and 
buried underground or suspended overhead. 
The branch and lamp conductors or ** leads " are 
finer wires of copper, insulated with india-rubber 
or silk. 

The current of an installation or section of 
one is made and broken at will by means of a 
"switch " or key turned by hand. It is simply a 



I20 



THE STORY OF ELECTRICITY. 



series of metal contacts insulated from each other 
and connected to the conductors, with a sHding 
contact connected to the dynamo which travels 
over them. To guard against an excess of cur- 
rent on the lamps, *' cut-outs," or safety-fuses, are 
inserted between the switch and the conductors, 
or at other leading points in the circuit. They 
are usually made of short slips of metal foil or 
wire,, which melt or deflagrate when the current 
is too strong, and thus interrupt the circuit. 




Fig. 69. — Electrical Phosphorescence. 



There is some prospect of the luminosity ex- 
cited in a vacuum tube by the alternating currents 
from a dynamo or an induction coil becoming 
an illuminant. Crookes has obtained exquisitely 
beautiful glows by the phosphorescence of gems 



ELECTRIC LIGHT AND HEAT. 



121 



and other minerals in a vacuum bulb like that 
shown in figure 69, where A and B are the metal 
electrodes on the outside of the glass. A heap of 
diamonds from various countries emit red, orange, 
yellow, green, and blue rays. Ruby, sapphire, 
and emerald give a deep red, crimson, or lilac 
phosphorescence, and sulphate of zinc a magnifi- 
cent green glow. Tesla has also shown that 
vacuum bulbs can be lit inside without any out- 
side connection with the current, by means of an 
apparatus like that shown in figure 70, where D 
is an alternating dynamo, C a condenser, F S the 
primary and secondary coils of a sparking trans- 
former, T T two metal sheets or plates, and B B 
the exhausted bulbs. The alternating or see-saw 




T B 

Fig. 70. — The Ideal Illuminant. 



current in this case charges the condenser and 
excites the primary coil P, while the induced cur- 
rent in the secondary coil 6" charges the terminal 
plates T T. So long as the bulbs or tubes are 
kept within the space between the plates, they 
are filled with a soft radiance, and it is easy to 



122 



THE STORY OF ELECTRICITY. 



see that if these plates covered the opposite walls 
of a room, the vacuum lamps would yield a light 
in any part of it. 

Electric heating bids fair to become almost as 
important as electric illumination. When the arc 
was first discovered it was noticed that platinum, 
gold, quartz, ruby, and diamond — in fine, the 
most refractory minerals — were melted in it, and 
ran like wax. Ores and salts of the metals were 
also vapourised, and it was clear that a powerful 
engine of research had been placed in the hands 
of the chemist. As a matter of fact, the tempera- 
ture of the carbons 
in the arc is com- 
parable to that of 
the Sun. It meas- 
ures 5000 to 10,000° 
Fahrenheit, and is 
the highest artifi- 
cial heat known. Sir 
William Siemens was 
among the first to 
make an electric fur- 
nace heated by the 
arc, which fused and 
vapourised metallic ores, so that the metal could 
be extracted from them. Aluminium, chromium, 
and other valuable metals are now smelted by its 
means, and rough brilliants such as those found 
in diamond mines and meteoric stones have been 
crystallised from the fumes of carbon, like hoar 
frost in a cold mist. 

The electric arc is also applied to the welding 
of wires, boiler plates, rails, and other metal work, 
by heating the parts to be joined and fusing them 
together. 




Fig. 71. 



ELECTRIC LIGHT AND HEAT. 12;} 

Cooking and heating by electricity are coining 
more and more into favour, owins^ to their clean- 





FiG. 72. 



Fig. 73. 



liness and convenience. Kitchen ranges, includ- 
ing ovens and grills, entirely heated by the elec- 
tric current, are finding 
their way into the best 
houses and hotels. Most 
of these are based 
on the principle 
of incandescence, 
the current heat- 
ing a fine wire or 
other conductor 
of high resist- 
ance in passing 
through it. Fig- 
ure 71 represents an elec- 
tric kettle of this sort, 
which requires no out- 
side fire CO boil it, since 
the current flows through 
fine wires of platinum or 
some highly resisting 
metal embedded in fire- 
proof insulating cement 
in its bottom. Figures 
72 and 73 are a sauce-pan and a flat-iron heated 




Fig. 



74. 




124 THE STORY OF ELECTRICITY. 

in the same way. Figure 74 is a cigar-lighter for 
smoking rooms, the fusee F consisting of short 
platinum wires, which be- 
come red-hot when it is 
unhooked, and at the same 
time the lamp L is auto- 
matically lit. Figure 75 is 
an electric radiator for 
heating rooms and passa- 
ges, after the manner of 
stoves and hot water pipes. 
Quilts for beds, warmed 
by fine wires inside, 
have also been brought 
out, a constant temper- 
ature being maintained 
by a simple regulator, 
and it is not unlikely Fig. 75. 

that personal clothing 

of the kind will soon be at the service of invalids 
and chilly mortals, more especially to make them 
comfortable on their travels. 

An ingenious device places an electric heater 
inside a hot water bag, thus keeping it at a uni- 
form temperature for sick-room and hospital use. 



CHAPTER VIII. 

ELECTRIC POWER. 

On the discovery of electromagnetism (Chap. 
IV.), Faraday, Barlow, and others devised ex- 
perimental apparatus for producing rotary motion 
from the electric current, and in 1831, Joseph 



ELECTRIC POWER. 



125 



Henry, the famous American electrician, invented 
a small electromagnetic engine or motor. These 
early machines were actuated by the current from 
a voltaic battery, but in the middle of the century 
Jacobi found that a dynamo-electric generator 
can also work as a motor, and that by coupling 
two dynamos in circuit — one as a generator, the 
(Uher as a motor — it was possible to transmit me- 
chanical power to any distance by means of elec- 
tricity. Figure 76 is a diagram of a simple cir- 
cuit for the transmission of power, where j9 is the 

Fig. 76. 

technical symbol for a dynamo as a generator, 
having its poles (-f and — ) connected by wire to 
the poles of J/, the distant dynamo, as a motor. 
The generator D is driven by mechanical energy 
from any convenient source, and transforms it 
into electric energy, which flows through the cir- 
cuit in the direction of the arrows, and, in trav- 
ersing the motor M, is re-transformed into me- 
chanical energy. There is, of course, a certain 
waste of energy in the process, but with good 
machines and conductors, it is not more than 10 
to 25 per cent., or the "efficiency" of the instal- 
lation is from 75 to 90 per cent. — that is to say, 
for every 100 horse-power put into the generator, 
from 75 to 90 horse-power are given out again by 
the motor. 

It was not until 1870, when Gramme had im- 
proved the dynamo, that power was practically 



126 THE STORY OF ELECTRICITY. 

transmitted in this way, and applied to pumping 
water, and other work. Since then great progress 
has been made, and electricity is now recognised, 
not only as a rival of steam, but as the best 
means of distributing steam, wind, water, or any 
other power to a distance, and bringing it to bear 
on the proper point. 

The first electric railway^ or, rather, tramway, 
was built by Dr. Werner von Siemens at Berlin in 
1879, ^^d was soon followed by many others. 
The wheels of the car were driven by an electric 
motor drawing its electricity from the rails, which 
were insulated from the ground, and being con- 
nected to the generator, served as conductors. It 
was found very difficult to insulate the rails, and 
keep the electricity from leaking to the ground, 
however, and at the Paris Electrical Exhibition 
of 1881, von Siemens made a short tramway in 
which the current was drawn from a bare copper 
conductor running on poles, like a telegraph wire, 
along the line. 

The system will be understood from figure 77, 
where L is the overhead conductor joined to the 
positive pole of the dynamo or generator in the 
power house, and C is a rolling contact or trolley 
wheel travelling with the car and connected by 
the wire W to an electric motor M under the car, 
and geared to the axles. After passing through 
the motor the current escapes to the rail i? by a 
brush or sliding contact C\ and so returns to the 
negative pole of the generator. A very general 
way is to allow the return current to escape to 
the rails through the wheels. Many tramways, 
covering thousands of miles, are now worked 
on this plan in the United States. At Bangor, 
Maine, a modification of it is in use whereby the 



ELECTRIC POWER. 



127 



conductor is divided into sections, alternately 
connected to the positive and negative poles of 
two generators, coupled together as in the ** three- 
wire system" of electric lighting (page 119), 




Fig. 77. — An Electric Railway. 

their middle poles being joined to the earth — that 
is to say, the rails. It enables two cars to be run 
on the same line at once, and with a considerable 
saving of copper. 

To make the car independent of the conductor 
L for a short time, as in switching, a battery of 
accumulators B may be added and charged from 
the conductor, so that when the motor is discon- 
nected from the conductor, the discharge from the 
accumulator may still work it and drive the wheels. 

Attempts have been made to run tramcars 
with the electricity supplied by accumulators 
alone, but the system is not economical owing to 
the dead weight of the cells, and the periodical 
trouble of recharging them at the genera^ting sta- 
tion. 



128 THE STORY OF ELECTRICITY. 

On heavy railroads worked by electricity the 
overhead conductor is replaced by a third rail 
along the middle of the track, and insulated from 
the ground. In another system the middle con- 
ductor is buried underground, and the current is 
tapped at intervals by the motor connecting with 
it for a moment by means of spring contacts as 
the car travels. In each case, however, the outer 
rails serve as the return conductors. 

Another system puts one or both the conduc- 
tors in a conduit underground, the trolley pole 
entering through a narrow slot similar to that 
used on cable roads. 

The first electric carriages for ordinary roads 
were constructed m 1889 by Mr. Magnus Volk of 
Brighton. Figure 78 represents one of these 
made for the Sultan of Turkey, and propelled by 
a one-horse-power Immisch electric motor, geared 
to one of the hind wheels by means of a chain. 
The current for the motor was supplied by thirty 
^* E. P. S." accumulators stow^ed in the body of the 
vehicle, and of sufficient power to give a speed of 
ten miles an hour. The driver steers with a hand 
lever as shown, and controls the speed by a switch 
in front of him. 

Vans, bath chairs, and tricycles are also driven 
by electric motors, but the weight of the battery 
is a drawback to their use. 

In or about the year 1839, Jacobi sailed an 
electric boat on the Neva, with the help of an 
electromagnetic engine of one horse-power, fed 
by the current from a battery of Grove cells, and 
in 1882 a screw launch, carrying several passen- 
gers, and propelled by an electric motor of three 
horse-power, worked by forty-five accumulators, 
was tried on the Thames. Being silent and 



I 



ELECTRIC POWER. 



smokeless in its action, the electric boat soon 
came into favour, and there is now quite a flotilla 




on the river, with power stations for charging 
the accumulators at various points along the 
banks. 

Figure 79 illustrates the interior of a hand- 
some electric launch, the Lady Cooper^ built for 
the " E. P. S.," or Electric Power Storage Com- 
pany. An electric motor in the after part of the 
hull is coupled directly to the shaft of. the screw 
propeller, and fed by " E. P. S." accumulators in 
teak boxes lodged under the deck amidships. 
The screw is controlled by a switch, and the 
rudder by an ordinary helm. The cabin is seven 
feet long, and lighted by electric lamps. Alarm 

9 



130 THE STORY OF ELECTRICITY. 

signals are given by an electric gong, and a 
search-light can be brought into operation when- 
ever it is desirable. The speed attained by the 
Lady Cooper is from ten to fifteen knots. 

M. Goubet, a Frenchman, has constructed a 
submarine boat for discharging torpedoes and 




Fig. 79. — An Electric Launch. 

exploring the sea bottom, which is propelled by 
a screw and an electric motor fed by accumula- 
tors. It can travel entirely under water, below 
the agitation of the waves, where sea-sickness is 
impossible, and the inventor hopes that vessels 
of the kind will yet carry passengers across the 
Channel. 

The screw propeller of the Edison and Sim's 
torpedo is also driven by an electric motor. In 
this case the current is conveyed from the ship 
or fort which discharges the torpedo by an in- 
sulated conductor running off a reel carried by 
•the torpedo, the ** earth " or return half of the 
circuit being the sea-water. 

All sorts of machinery are now worked by the 
electric motor — for instance, cranes, elevators, 
capstans, rivetters, lathes, pumps, chaff-cutters, 
and saws. Of domestic appliances, figure 80 
shows an air propeller or ventilation fan, where 
i^ is a screw-like fan attached to the spindle of 
the motor J/, and revolving with its armature. 
Figure 81 represents a Trouve motor working a 
sewing-machine, where iV^is the motor which gears 



ELECTRIC POWER. 



with P the driving axle of the machine. Figure 
82 represents a fine drill actuated by a Griscom 
motor. The motor J/ is sus- 
pended from a bracket ABC 
by the tackle D E, and trans- 
mits the rotation of its arm- 
ature by a flexible shaft 6* T 
to the terminal 
drill O, which can 
be applied at any 
point, and is use- 
ful in boring teeth. 
Now that elec- 
tricity is manufac- 
tured and distrib- 
uted in towns and 
villages for the 
electric light, it is 
more and more employed for 
driving the lighter machine- 
ry. Steam, however, is more 
economical on a large scale, 
Fig. 80.— An Electric Fan. and Still Continues to be used 
in great factories for the 
heavier machinery. Nevertheless a day is coming 
when coal, instead of being carried by rail to dis- 
tant works and cities, will be burned at the pit 
mouth, and its heat transformed by means of en- 
gines and dynamos into electricity for distribution 
to the surrounding country. I have shown else- 
where that peat can be utilised in a similar man- 
ner, and how the great Bog of Allen is virtually a 
neglected gold field in the heart of Ireland.* The 
sunshine of deserts, and perhaps the electricity of 
the atmosphere, but at all events the power of 

* The Ximtcenfh Cintury for December 1^94. 




132 



THE STORY OF ELECTRICITY. 



winds, waves, and waterfalls are also destined to 
whirl the dynamo, and yield us light, heat, or mo- 
tion. Much has already been done in this direc- 
tion. In 1891 the power of turbines driven by the 




Fig. 81. — An Electric Sewing Machine. 



Falls of Neckar at Lauffen was transformed into 
electricity, and transmitted by a small wire to the 
Electrical Exhibition of Frankfort-on-the-Main, 
117 miles away. The city of Rome is now lighted 
from the Falls of Tivoli, 16 miles distant. The 
finest cataract in Great Britain, the Falls of Foyers, 
in the Highlands, which persons of taste and cul- 
ture wished to preserve for the nation, is being 
sacrificed to the spirit of trade, and deprived of 
its waters for the purpose of generating electricity 
to reduce aluminium from its ores. 

The great scheme recently completed for util- 
izing the power of Niagara Falls by means of 
electricity is a triumph of human enterprise which 



ELECTRIC POWER. 



outrivals some of the bold creations of Jules 
Verne. 

When in 167S the French missionaries La Salle 
and Hennepin discovered the stupendous cataract 
on the Niagara River 
between Lake Onta- 
rio and Lake Erie, 
the science of elec- 
tricity was in its ear- 
ly infancy, and little 
more was known 
about the mysterious 
force which is per- 
forming miracles in 
our day than its man- 
ifestation on rubbed 
amber, sealing-wax, 
glass, and other bod- 
ies. Nearly a hun- 
dred years had still 
to pass ere Franklin 
should demonstrate 
the identity of the electric fire with lightning, and 
nearly another hundred before Faraday should 
reveal a mode of generating it from mechanical 
power. Assuredly, neither La Salle nor his con- 
temporaries ever dreamed of a time when the 
water-power of the Falls w^ould be distributed by 
means of electricity to produce light or heat and 
serve all manner of industries in the surrounding 
district. The awestruck Iroquois Indians had 
named the cataract "Oniagahra," or Thunder of 
the Waters, and believed it the dwelling-place of 
the Spirit of Thunder. This j)oetical name is 
none the less appropriate now that the modern 
electrician is preparing to draw his lightnings from 




Fig. 82.— An Electric Drill. 



134 THE STORY OF ELECTRICITY. 

its waters and compel the ge?ttus loci to become 
his willing bondsman. 

The Falls of Niagara are situated about 
twenty-one miles from Lake Erie, and fourteen 
miles from Lake Ontario. At this point the Ni- 
agara River, nearly a mile broad, flowing between 
level banks, and parted by several islands, is sud- 
denly shot over a precipice 170 feet high, and 
making a sharp bend to the north, pursues its 
course through a narrow gorge towards Lake On- 
tario. The Falls are divided at the brink by Goat 
Island, whose primeval woods are still thriving in 
their spray. The Horseshoe Fall on the Canadian 
side is 812 yards, and the American Falls on the 
south side are 325 yards wide. For a consider- 
able distance both above and below the Falls the 
river is turbulent with rapids. 

The water-power of the cataract has been em- 
ployed from olden times. The French fur-traders 
placed a mill beside the upper rapids, and the 
early British settlers built another to saw the tim- 
ber used in their stockades. By-and-by, the 
Stedman and Porter mills were established below 
the Falls; and subsequently, others which derived 
their water-supply from the lower rapids by means 
of raceways or leads. Eventually, an open hy- 
draulic canal, three-fourths of a mile long, was 
cut across the elbow of land on the American 
side, through the town of Niagara Falls, between 
the rapids above and the verge of the chasm below 
the Falls, where, since 1874, a cluster of factories 
has arisen, which discharge their spent water over 
the cliff in a series of cascades almost rivalling 
Niagara itself. This canal, which only taps a 
mere drop from the ocean of power that is run- 
ning to waste, has been utilised to the full ; and 



ELECTRIC POWER. 1 35 

the decrease of water-privileges in the New Eng- 
land States, owing to the clearing of the forests 
and settlement of the country, together with the 
growth of the electrical industries, have led to a 
further demand on the resources of Niagara. 

With the example of Minneapolis, which draws 
the power for its many mills from the Falls of St. 
Anthony, in the Mississippi River, before them, a 
group of far-seeing and enterprising citizens of 
Niagara Falls resolved to satisfy this requirement 
by the foundation of an industrial city in the 
neighbourhood of the Falls. They perceived that 
a better site could nowhere be found on the 
American Continent. Apart from its healthy air 
and attractive scenery, Niagara is a kind of half- 
way house between the East and West, the con- 
suming and the producing States. By the Erie 
Canal at Tonawanda it commands the great water- 
way of the Lakes and the St. Lawrence. A sys- 
tem of trunk railways from different parts of the 
States and Canada are focussed there, and cross 
the river by the Cantilever and Suspension bridges 
below the Falls. The New York Central and 
Hudson River, the Lehigh Valley, the Buffalo, 
Rochester, and Pittsburgh, the Michigan Central, 
and the Grand Trunk of Canada, are some of these 
lines. Draining as it does the great lakes of the 
interior, which have a total area of 92,000 square 
miles, with an aggregate basin of 290,000 square 
miles, the volume of water in the Niagara River 
passing over the cataract every second is some- 
thing like 300,000 cubic feet ; and this, with a fall 
of 276 feet from the head of the upper rapids to 
the whirlpool rapids below, is equivalent to about 
nine million, or, allowing for waste in the turbines, 
say, seven million horse-power. Moreover, the 



J 36 THE STORY OF ELECTRICITY. 

great lakes discharging into each other form a 
chain of immense reservoirs, and the level of the 
river being little affected by flood or drought, the 
supply of pure water is practically co^nstant all 
the year round. Mr. R. C. Reid has shown that 
a rainfall of three inches in twenty-four hours 
over the basin of Lake Superior would take 
ninety days to run off into Lake Huron, which, 
with Lake Michigan, would take as long to over- 
flow into Lake Erie ; and, therefore, six months 
would elapse before the full effect of the flood 
was expended at the Falls. 

The first outcome of the movement was the 
Niagara River Hydraulic Power and Sewer Com- 
pany, incorporated in 1886, and succeeded by the 
Niagara Falls Power Company. The old plan of 
utilising the water by means of an open canal was 
unsuited to the circumstances, and the company 
adopted that of the late Mr. Thomas Evershed, 
divisional engineer of the New York State Canals. 
Like the other, it consists in tapping the river 
above the Falls, and using the pressure of the 
water to drive the number of turbines, then re- 
storing the water to the river below the Falls; 
but instead of a surface canal, the tail-race is a 
hydraulic tunnel or underground conduit. To this 
end some fifteen hundred acres of spare land, 
having a frontage just above the upper rapids, was 
quietly secured at the low price of three hundred 
dollars an acre; and we believe its rise in value 
owing to the progress of the works is such that 
a yearly rental of two hundred dollars an acre can 
even now be got for it. This land has been laid 
out as an industrial city, with a residential quar- 
ter for the operatives, wharves along the river, 
and sidings or short lines to connect with the 



Electric power. 137 

trunk railways. In carrying out their purpose 
the company has budded and branched into other 
companies — one for the purchase of the land ; 
another for making the railways; and a third, 
the Cataract Construction Company, which is 
charged with the carrying out of the engineer- 
ing works, for the utilisation of the water-power, 
and is therefore the most important of all. A 
subsidiary company has also been formed to 
transmit by electricity a portion of the available 
power to the city of Buffalo, at the head of the 
Niagara River, on Lake Erie, some tw^enty miles 
distant. All these affiliated bodies are, however, 
under the directorate of the Cataract Construc- 
tion Company; and amongst those who have 
taken the most active part in the work we may 
mention the president, Mr. E. D. Adams; Pro- 
fessor Coleman Sellers, the consulting engineer ; 
and Professor George Forbes, F. R. S., the con- 
sulting electrical engineer, a son of the late Prin- 
cipal Forbes of Edinburgh. 

In securing the necessary right of way for the 
hydraulic tunnel or in the acquisition of land, 
the Company has shown consummate tact. A 
few proprietors declined to accept its terms, and 
the Company selected a parallel route. Having 
obtained the right of way for the latter, it in- 
formed the refractory owners on the first line of 
their success, and intimated that the Company 
could now dispense with that. On this the 
sticklers professed their willingness to accept 
the original terms, and the bargain was con- 
cluded, thus leaving the Company in possession 
of the rights of way for two tunnels, both of 
which they propose to utilise. 

The liberal policy of the directors is deserving 



138 THE STORY OF ELECTRICITY. 

of the highest commendation. They have risen 
above mere *' chauvinism," and instead of nar- 
rowly confining the work to American engineers, 
they have availed themselves of the best scientific 
counsel which the entire world could afford. The 
great question as to the best means of distribut- 
ing and applying the power at their command 
had to be settled ; and in 1890, after Mr. Adams 
and Dr. Sellers had made a visit of inspection 
to Europe, an International Commission was ap- 
pointed to consider the various methods sub- 
mitted to them, and award prizes to the success- 
ful competitors. Lord Kelvin (then Sir William 
Thomson) was the president, and Professor W. 
C. Unwin, the well-known expert in hydraulic 
engineering, the secretary, while other members 
were Professor Mascart of the Institute, a lead- 
ing French electrician ; Colonel Turretini of 
Geneva, and Dr. Sellers. A large number of 
schemes were sent in, and many distinguished 
engineers gave evidence before the Commission. 
The relative merits of compressed air and elec- 
tricity as a means of distributing the power were 
discussed, and on the whole the balance of opinion 
was in favour of electricity. Prizes of two hun- 
dred and two hundred and fifty pounds were 
awarded to a number of firms who had submitted 
plans, but none of these were taken up by the 
Company. The impulse turbines of Messrs. 
Faesch & Piccard, of Geneva, who gained a prize 
of two hundred and fifty pounds, have, how^ever, 
been adopted since. It is another proof of the 
determination of the Company to procure the 
best information on the subject, regardless of 
cost, that Professor Forbes had carte blcmche to 
go to any part of the world and make a report 



ELECTRIC POWER. 139 

on any system of electrical distribution which he 
might think fit. 

With the selection of electricity another ques- 
tion arose as to the expediency of employini^ 
continuous or alternating currents. At that tmie 
continuous currents were chiefly in vogue, and it 
speaks well for the sagacity and prescience of 
Professor Forbes that he boldly advocated the 
adoption of alternating currents, more especially 
for the transmission of power to Buffalo. His 
proposals encountered strong opposition, even in 
the highest quarters; but since then, partly 
owing to the striking success of the Lauffen to 
Frankfort experiment in transmitting power by 
alternating currents over a bare wire on poles 
a distance of more than a hundred miles, the 
directors and engineers have come round to his 
view of the matter, and alternating currents have 
been employed, at all events for the Buffalo line, 
and also for the chief supply of the industrial 
city. Continuous currents, flowing always in the 
same direction, like the current of a battery, can, 
it is true, be stored in accumulators, but they 
cannot be converted to higher or lower pressure 
in a transformer. Alternating currents, on the 
other hand, which see-saw in direction many 
times a second, cannot be stored in accumulators, 
but they can be sent at high pressure along a very 
fine wire, and then converted to higher or lower 
pressures where they are wanted, and even to con- 
tinuous currents. Each kind, therefore, has its 
peculiar advantages, and both will be employed 
to some extent. 

With regard to the engineering works, the 
hydraulic tunnel starts from the bank of the 
river where it is navigable, at a point a mile and 



140 THE STORY OF ELECTRICITY. 

a half above the Falls, and after keeping by the 
shore, it cuts across the bend beneath the city of 
Niagara Falls, and terminates below the Suspen- 
sion Bridge under the Falls at the level of the 
water. It is 6700 yards long, and of a horseshoe 
section, 19 feet wide by 21 feet high. It has been 
cut 160 feet below the surface through the lime- 
stone and shale, but is arched with brick, having 
rubble above, and at the outfall is lined on the 
invert or under side with iron. The gradient is 
36 feet in the mile, and the total fall is 205 feet, of 
which 140 feet are available for use. The capac- 
ity of the tunnel is 100,000 horse-power. In the 
lands of the company it is 400 feet from the mar- 
gin of the river, to which it is connected by a 
canal, which is over 1500 feet long, 500 feet wide 
at the mouth, and 12 feet deep. 

Out of this canal, head-races fitted with sluices 
conduct the water to a number of wheel-pits 160 
feet deep, which have been dug near the edge of 
the canal, and communicate below with the tun- 
nel. At the bottom of each wheel-pit a 5000 
horse-power Girard double turbine is mounted on 
a vertical shaft, which drives a propeller shaft 
rising to the surface of the ground ; a dynamo of 
5000 horse-power is fixed on the top of this shaft, 
and so driven by it. The upward pressure of the 
water is ingeniously contrived to relieve the 
foundation of the weight of the turbine shaft and 
dynamo. Twenty of these turbines, which are 
made by the I. P. Morris Company of Philadel- 
phia, from the designs of Messrs. Faesch and 
Piccard, will be required to utilize the full capac- 
ity of the tunnel. 

The company possesses a strip of land extend- 
ing two miles along the shore; and in excavating 



ELECTRIC POWER. 141 

the tunnel a coffer-dam was made with the ex- 
tracted rock, to keep the river from flooding the 
works. This dam now forms part of a system by 
which a tract of land has been reclaimed from the 
river. Part of it has already been acquired by 
the Niagara Paper Pulp Company, which is build- 
ing gigantic factories, and will employ the tail- 
race or tunnel of the Cataract Construction Com- 
pany. Wharfs for the use of ships and canal 
boats will also be constructed on this frontage. 
By land and water the raw materials of the West 
will be conveyed to the industrial town which is 
now coming into existence ; grain from the prai- 
ries of Illinois and Dakota; timber from the for- 
ests of Michigan and Wisconsin ; coal and copper 
from the mines of Lake Superior ; and what not. 
It is expected that one industry having a seat 
there will attract others. Thus, the pulp mills 
will bring the makers of paper wheels and bar- 
rels ; the smelting of iron w411 draw foundries 
and engine works ; the electrical refining of cop- 
per will lead to the establishment of wire-works, 
cable factories, dynamo shops, and so on. Alu- 
minum, too, promises to create an important in- 
dustry in the future. In the meantime, the Cata- 
ract Construction Company is about to start an 
electrical factory of its own, which will give em- 
ployment to a large number of men. It has also 
undertaken the water supply of the adjacent city 
of Niagara Falls. The Cataract Electric Com- 
pany of Buffalo has obtained the exclusive right 
to use the electricity transmitted to that city, 
and the line will be run in a subway. This 
underground line will be more expensive to make 
than an overhead line, but it will not recjuire to 
be renewed every eight to fifteen years, and it 



!l 



142 THE STORY OF ELECTRICITY. 

will not be liable to interruption from the heavy 
gales that sweep across the lakes, or the weight 
of frozen sleet : moreover, it will be more easily 
inspected, and quite safe for the public. We 
should also add that, in addition to the contem- 
plated duplicate tunnel of 100,000 horse-power, 
the Cataract Construction Company owns a con- 
cession for utilising 250,000 horse-power from the 
Horseshoe Falls on the Canadian side in the same 
manner. It has thus a virtual monopoly of the 
available water-power of Niagara, and the pro- 
moters have not the least doubt that the enter- 
prise will be a great financial success. Already 
the Pittsburg Reduction Company have begun to 
use the electricity in reducing aluminum from 
the mineral known as bauxite, an oxide of the 
metal, by means of the electric furnace. 

Another portion of the power is to be used to 
produce carbide of calcium for the manufacture 
of acetylene gas. At a recent electrical exhibition 
held in New York city a model of the Niagara 
plant was operated by an electric current brought 
from Niagara, 450 miles distant; and a collection 
of telephones were so connected that the spec- 
tator could hear the roar of the real cataract. 

Thanks to the foresight of New York State 
and Canada, the scenery of the Falls has been 
preserved by the institution of public parks, and 
the works in question will do nothing to spoil it, 
especially as they will be free from smoke. Mr. 
Bogarts, State Engineer of New York, estimates 
that the water drawn from the river will only 
lower the mean depth of the Falls about two 
inches, and will therefore make no appreciable 
difference in the view. Altogether, the enter- 
prise is something new in the history of the 



MINOR USES OF ELECTRICITY. 



M3 



world. It is not only the grandest application of 
electrical power, but one of the most remarkable 
feats in an age when romance has become science, 
and science has become romance. 



CHAPTER IX. 

MINOR USES OF ELECTRICITY. 

The electric *' trembling bell," now in common 
use, was first invented by John Mirand in 1850. 
Figure St, shows the scheme of the circuit, where 




P 

Fig. 83. — An Electric Trembling Bell. 



^ is a small battery, say two or three " dry " or 
Leclanche cells, joined by insulated wire to P, 
a press-button or contact key, and G an electro- 
magnetic gong or bell. On pressing the button 
P, a spring contact is made, and the current 
flowing through the circuit strikes the bell. The 
action of the contact key will be understood 
from figure 84, where P is the press-button 
removed to show the underlying mechanism, 
which is merely a metal spring A over a metal 



144 



THE STORY OF ELECTRICITY. 



plate B. The spring is connected by wire to a 
pole of the battery, and the plate to a terminal 
or binding screw of the bell, or vice versa. When 





Fig. 84. 



the button P is pressed by the finger the spring 
is forced against the plate, the circuit is made, 
and the bell rings. On releasing the button it 
springs back, the circuit is broken, and the bell 
stops. 

Figure 85 shows the inner mechanism of the 
bell, which consists of a double-poled electro- 
magnet M, having a soft iron armature A hinged 
on a straight spring or tongue 6', with one end 
fixed, and the other resting against a screw con- 
tact T, The hammer H projects from the arma- 
ture beside the edge of the gong E. 

In passing through the instrument the current 
proceeds from one terminal, say that on the right, 
by the wire W lo the screw contact 7", and thence 
by the spring S through the bobbins of the elec- 
tromagnet to the other terminal. The electro- 
magnet attracts the armature A^ and the hammer 
H strikes the gong ; but in the act the spring S 
is drawn from the contact T, and the circuit is 
broken. Consequently the electromagnet, no 



MINOR USES OF ELECTRICITY. 



M5 



longer excited, lets the armature go, and the 
spring leaps back against the contact 7", with- 




FlG. 85. 



drawing the hammer from the gong. But the in- 
strument is now as it was at first, the current again 
flows, and the hammer strikes the gong, only to 
fly back a second time. In this way, as long as 
the button is pressed by the operator, the hammer 
will continue to tap the bell and give a ringing 
sound. Press-buttons are of various patterns, and 
either affixed to the wall or inserted in the handle 
of an ordinary bell-pull, as shown in figure 86. 
10 



146 



THE STORY OF ELECTRICITY. 



The ordinary electric bell actuated by a bat- 
tery is liable to get out of order owing to the 
battery spending its force, or to the 
contacts becoming dirty. Magneto- 
electric bells have, therefore, been 
introduced of late years. With these 
no battery or interrupting contacts 
are required, since the bell-pull or 
press-button is made in the form of 
a small dynamo which generates the 
current when it is pulled or pushed. 
Figure 87 illustrates a form of this 
apparatus, where M F is the bell- 
pull and B the bell, these being con- 
nected by a double wire W^ to con- 
vey the current. The bell-pull con- 
sists of a horseshoe magnet M, hav- 
ing a bobbin of insulated wire be- 
tween its poles, and mounted on a 
spindle. When the key F is turned 
round by the hand, the bobbin moves 
in the magnetic field between the 
poles of the magnet, and the current 
thus generated circulates in the wires 
W, and passing through an electro- 
magnet under the bell, attracts its armature, and 
strikes the hammer on the bell. Of course the 
bell may be placed at any distance from the gen- 
erator. In other types the current is generated 
and the bell rung by the act of pulling, as in a 
common house-bell. 

Electric bells in large houses and hotels are 
usually fitted up with indicators, as shown in 
figure ^2>, which tell the room from which the 
call proceeds. They are serviceable as instan- 
taneous signals, annunciators, and alarms in many 




Fig. 86. 



MINOR USES OF ELECTRICITY. 



M7 



different ways. An outbreak of fire can be an- 
nounced by causing the undue rise of tempera- 




FlG. 87. 

tare to melt a piece of tallow or fusible metal, 
and thus release a weight, which falls on a press- 
button, and closes the circuit of an electric bell. 
Or, the rising temperature may expand the mer- 
cury in a tube like that of a thermometer until it 
connects two platinum wires fused through the 
glass and in circuit with a bell. Some employ a 
curving bi-metallic spring to make the necessary 
contact. The spring is made by soldering strips 
of brass and iron back to back, and as these 
metals expand unequally when heated, the spring 
is deformed, and touches the contact which is 
connected in the circuit, thus permitting the cur- 



i\ t 



148 



THE STORY OF ELECTRICITY. 



rent to ring the bell. A still better device, how- 
ever, is a small box containing a thin metallic 

diaphragm, which 
expands with the 
heat, and sagging 
in the centre, touch- 
es a contact screw, 
thus completing the 
circuit, and allow- 
ing the current to 
pass. 

These automatic 
or self-acting fire- 
alarms can, of 
course, be con- 
nected in the cir- 
cuit of the ordinary 
street fire - alarms, 
which are usually 
worked by pulling 
a handle to make 
the necessary con- 
tact. 

From what has 
been said, it will be 
easy to understand how the stealthy entrance of 
burglars into a house can be announced by an 
electric bell or warning lamp. If press-buttons or 
contact-keys are placed on the sashes of the win- 
dows, the posts of the door, or the treads of the 
stair, so that when the window or door is opened, 
or the tread bends under the footstep, an electric 
circuit is closed, the alarm will be given. Of 
course, the connections need only be arranged 
when the device is wanted. Shops and offices 
can be guarded by making the current show a 




Fig. 88. 



MINOR USES OF ELECTRICITY. 149 

red light from a lamp hung in front of the prem- 
ises, so that the night watchman can see it on 
his beat. This can readily be done by adjusting 
an electromagnet to drop a screen of red glass 
before the flame of the lamp. Safes and show- 
cases forcibly opened can be made to signal the 
fact, and recently in the United States a thief was 
photographed by a flashlight kindled in this way, 
and afterwards captured through the likeness. 

The level of water in cisterns and reservoirs 
can be told in a similar manner by causing a 
float to rise with the water and make the re- 
quired contact. The degree of frost in a con- 
servatory can also be announced by means of 
the mercury *^ thermostat," already described, 
or some equivalent device. There are, indeed, 
many actual or possible applications of a similar 
kind. 

The Massey log is an instrument for telling 
the speed of a ship by the revolutions of a *^ fly " 
as it is towed through the water, and by making 
the fly complete a circuit as it revolves the num- 
ber of turns a second can be struck by a bell on 
board. In one form of the "electric log," the 
current is generated by the chemical action of 
zinc and copper plates attached to the log, and 
immersed in the sea water, and in others pro- 
vided by a battery on the ship. 

Captain M'Evoy has invented an alarm for 
torpedoes and torpedo boats, which is a veritable 
watchdog of the sea. It consists of an iron bell- 
jar inverted in the water, and moored at a depth 
below the agitation of the waxes. In the upper 
part of the jar, where the pressure of the air 
keeps back the water, there is a delicate needle 
contact in circuit with a battery and an electric 



t\ Jk 



150 THE STORY OF ELECTRICITY. 

bell or lamp, as the case may be, on the shore. 
Waves of sound passing through the water from 
the screw propeller of the torpedo, or, indeed, any 
ship, make and break the sensitive contact, and 
ring the bell or light the lamp. The apparatus 
is intended to alarm a fleet lying at anchor or a 
port in time of war. 

Electricity has also been employed to register 
the movements of weathercocks and anemometers. 
A few years ago it was applied successfully to 
telegraph the course marked by a steering com- 
pass to the navigating officer on the bridge. 
This was done without impeding the motion of 
the compass card by causing an electric spark to 
jump from a light pointer on the card to a series 
of metal plates round the bowl of the compass, 
and actuate an electric alarm. 

The '^ Domestic Telegraph," an American de- 
vice, is a little dial apparatus by which a citizen 
can signal for a policeman, doctor, messenger, or 
carriage, as well as a fire engine, by the simple act 
of setting a hand on the dial. 

Alexander Bain was the first to drive a clock 
with electricity instead of weights, by employing 
a pendulum having an iron bob. which was at- 
tracted to one side and the other by an electro- 
magnet, but as its rate depends on the constancy 
of the current, which is not easy to maintain, the 
invention has not come into general use. The 
" butterfly clock " of Lemoine, which we illustrate 
in figure 89, is an improved type, in which the bob 
of soft iron I^ swings to and fro over the poles 
of a double electro magnet M in circuit with a 
battery and contact key. When the rate is too 
slow the key is closed, and a current passing 
through the electromagnet pulls on the pendu- 



MINOR USES OF ELECTRICITY. 



151 



ight 



lum, thus correcting the clock. This is done by 
the ingenious device of Hipp, shown in figure 
90, where J/ is the electromagnet, P the iron 
bob, from which projects a wire bearing a 
vane B of mica in the shape 
of a butterfly. As the bob 
swings the wire drags over 
the hump of the metal spring 
6", and when the bob is going 
too slowly the wire thrusts 
the spring into contact with 
another spring 7" below, thus 
closing the circuit, and send- 
ing a current through the 
magnet M^ which attracts the 
bob and gives a fillip to the 
pendulum. 

Local clocks controlled 
from a standard clock by elec- 
tricity have been more suc- 
cessful in practice, and are 
employed in several towns — 
for example, Glasgow. Be- 
hind local dials are electro- 
magnets which, by means of 
an armature working a frame and ratchet wheel, 
move the hands forward every minute or half- 
minute as the current is sent from the standard 
clock. 

The electrical chronograph is an instrument 
for measuring minute intervals of time by means 
of a stylus tracing a line on a band of travelling 
paper or a revolving barrel of smoked glass. The 
current, by exciting an electromagnet, jerks the 
stylus, and the interval between two jerks is 
found from the length of the trace between them 




Fig. 89.— The Electric 
" Butterfly" Clock. 



152 



THE STORY OF ELECTRICITY. 



and the speed of the paper or smoked surface. 
Retarded clocks are sometimes employed as 
electric meters for registering the consumption 
of electricity. In these the current to be mea- 
sured flows through a coil beneath the bob of the 
pendulum, which is a magnet, and thus affects the 




rate. In other meters the current passes through 
a species of galvanometer called an ampere meter, 
and controls a clockwork counter. In a third 
kind of meter the chemical effect of the current 
is brought into play — that of Edison, for example, 
decomposing sulphate of copper, or more com- 
monly of zinc. 

The electric light is now used for signalling 
and advertising by night in a variety of ways. 
Incandescent lamps inside a translucent balloon, 
and their light controlled by a current key, as in 



MINOR USES OF ELECTRICITY. 



is: 



a telegraph circuit, so as to give long and short 
flashes, according to the Morse code, are em- 
ployed in the army. Signals at sea are also 
made by a set of red and white glow-lamps, 
which are combined according to the code in use. 
The powerful arc lamp is extremely useful as a 
*' search light," especially on men-of-war and 
fortifications, and it has also been tried in sig- 
nalling by projecting the beam on the clouds by 
way of a screen, and eclipsing it according to a 
given code. 

In 1879, Professor Graham Bell, the inventor 
of the speaking telephone, and Mr. Summer 
Tainter, brought out an ingenious apparatus 
called the photophone, by which music and 
speech were sent along a beam of light for 
several hundred yards. The action of the photo- 
phone is based on the peculiar fact observed in 
1^73 by Mr. J. E. Mayhew, that the electrical re- 
sistance of crystalline selenium diminishes when 
a ray of light falls upon it. Figure 91 shows 





tiG. 91. — The Photophone. 



how Bell and Tainter utilised this property in the 
telephone. A beam of sun or electric light, con- 
centrated by a lens Z, is reflected by a thin mirror 
J/, and after traversing another lens Z, travels 
to the parabolic reflector R, in the focus of 



154 THE STORY OF ELECTRICITY. 

which there is a selenium resistance in circuit 
with a battery B and two telephones T V . Now, 
when a person speaks into the tube at the back 
of the mirror J/, the light is caused to vibrate 
with the sounds, and a wavering beam falls on the 
selenium, changing its resistance to the cur- 
rent. The strength of the current is thus varied 
with the sonorous waves, and the words spoken 
by the transmitter are heard in the telephones 
by the receiver. The photophone is, however, 
more of a scientific toy than a practical instru- 
ment. 

Becquerel, the French chemist, found that 
two plates of silver freshly coated with silver 
from a solution of chloride of silver and plunged 
into water, form a voltaic cell which is sensitive 
to light. This can be seen by connecting the 
plates through a galvanometer, and allowing a 
ray of light to fall upon them. Other combina- 
tions of the kind have been discovered, and 
Professor Minchin, the Irish physicist, has used 
one of these cells to measure the intensity of 
starlight. 

The '' induction balance " of Professor Hughes 
is founded on the well-known fact that a current 
passing in one wire can induce a sympathetic 
current in a neighbouring wire. The arrange- 
ment will be understood from figure 92, w^here P 
and P^ are two similar coils or bobbins of thick 
wire in circuit with a battery B and a micro- 
phone My while S and S^ are two similar coils or 
bobbins of fine wire in circuit with a telephone 
T, It need hardly be said that when the micro- 
phone M is disturbed by a sound, the current in 
the primary coils P P^ will induce a correspond- 
ing current in the secondary coils S S^\ but the 



MINOR USES OF ELECTRICITV. 



ISS 



coils ^ S-i are so wound that the induction of /* 
on 6" neutrahses the induction of /^j on S^, and 
no current passes in the secondary circuit, hence 
no sound is heard in the telephone. When, how- 




Fig. 92. — The Induction Balance. 



ever, this balance of induction is upset by bring- 
ing a piece of metal — say, a coin — near one or 
other of the coils 6* S^, a sound will be heard in 
the telephone. 

The induction balance has been used as a 
'' Sonometer " for measuring the sense of hear- 
ing, and also for telling base coins. The writer 
devised a form of it for ^^ divining" the presence 
of gold and metallic ores which has been applied 
by Captain M'Evoy in his ^' submarine detector " 
for exploring the sea bottom for lost anchors and 
sunken treasure. When President Garfield was 
shot, the position of the bullet was ascertained 
by a similar arrangement. 

The microphone as a means of magnifying 
feeble sounds has been employed for localising 
the leaks in water pipes and in medical examina- 
tions. Some years ago it saved a Russian lady 
from premature burial by rendering the faint beat- 
ing of her heart audible. 



156 



THE STORY OF ELECTRICItV. 



Edison's electric pen is useful in copying let- 
ters. It works by puncturing a row of minute 
holes along the lines of the writing, and thus pro- 
ducing a stencil plate, which, when placed over a 
clean sheet of paper and brushed with ink, gives 
a duplicate of the writing by the ink penetrating 
the holes to the paper below. It is illustrated in 
figure 93, where F is the pen, consisting of a hol- 




FiG. 93. -The Electric Pen. 



low Stem in which a fine needle actuated by the 
armature of a small electromagnet plies rapidly 
up and down and pierces the paper. The current 
is derived from a small battery B^ and an inking 
roller like that used in printing serves to apply 
the ink. 

In 1878 Mr. Edison announced his invention 
of a machine for the storage and reproduction of 
speech, and the announcement was received with 
a good deal of incredulity, notwithstanding the 
partial success of Faber and others in devising 
mechanical articulators. The simplicity of Edison's 
invention when it was seen and heard elicited much 
admiration, and although his first instrument was 
obviously imperfect, it was nevertheless regarded 
as the germ of something better. If the words 
spoken into the instrument were heard in the first 



MINOR USES OF ELECTRICITY. 157 

place, the likeness of the reproduction was found 
to be unmistakable. Indeed, so faithful was the 
replica, that a member of the Academy of Sci- 
ences, Paris, stoutly maintained that it was due to 
ventriloquism or some other trickery. It was evi- 
dent, however, that before the phonograph could 
become a practical instrument, further improve- 
ments in the nicety of its articulation were re- 
quired. The introduction of the electric light di- 
verted Mr. Edison from the task of improving it, 
although he does not seem to have lost faith in 
his pet invention. During the next ten years he 
accumulated a large fortune, and was the princi- 
pal means of introducing both electric light and 
power to the world at large. This done, how- 
ever, he returned to his earlier love, and has at 
length succeeded in perfecting it so as to redeem 
his past promises and fulfil his hopes regard- 
ing it. 

The old instrument consisted, as is well known, 
of a vibrating tympan or drum, from the centre 
of which projected a steel point or stylus, in such 
a manner that on speaking to the tympan its 
vibrations would urge the stylus to dig into a 
sheet of tinfoil moving past its point. The foil 
was supported on a grooved barrel, so that the 
hollow of the groove behind it permitted the foil 
to give under the point of the stylus, and take a 
corrugated or wavy surface corresponding to the 
vibrations of the speech. Thus recorded on a 
yielding but somewhat stiff material, these undu- 
lations could be preserved, and at a future time 
made to deflect the point of a similar stylus, and 
set a corresponding diaphragm or tympan into vi- 
bration, so as to give out the original sounds, or 
an imitation of them. 



158 THE STORY OF ELECTRICITY. 

Tinfoil, however, is not a very satisfactory 
material on which to receive the vibrations in the 
first place. It does not precisely respond to the 
movements of the marking stylus in taking the 
impression, and does not guide the receiving sty- 
lus sufficiently well in reproducing sounds. Mr. 
Edison has therefore adopted wax in preference 
to it ; and instead of tinfoil spread on a grooved 
support, he now employs a cylinder of wax to 
take the print of the vibrations. Moreover, he 
no longer uses the same kind of diaphragm to 
print and receive the sounds, but employs a more 
delicate one for receiving them. The marking 
cylinder is now kept in motion by an electric 
motor, instead of by hand-turning, as in the earlier 
instrument. 

The new phonograph, which we illustrate in 
figure 94, is about the size of an ordinary sewing 
machine, and is of exquisite workmanship, the 
performance depending to a great extent on the 
perfection and fitness of the mechanism. It con- 
sists of a horizontal spindle S, carrying at one 
end the wax cylinder C, on which the sonorous 
vibrations are to be imprinted. Over the cylin- 
der is supported a diaphragm or tympan T, pro- 
vided with a conical mouthpiece M for speaking 
into. Under the tympan there is a delicate needle 
or stylus, with its point projecting from the centre 
of the tympan downwards to the surface of the 
wax cylinder, so that when a person speaks into 
the mouthpiece, the voice vibrates the tympan 
and drives the point of the stylus down into the 
wax, making an imprint more or less deep in ac- 
cordance with the vibrations of the voice. The 
cylinder is kept revolving in a spiral path, at a 
uniform speed, by means of an electric motor £y 



MINOR USES OF ELECTRICITY. 



^59 



fitted with a sensitive regulator and situated at 
the base of the machine. The result is that a deli- 




FiG. 94. — The Phonogjaph. 



cate and ridgy trace is cut in the surface of wax 
along a spiral line. This is the sound record, and 
by substituting a finer tympan for the one used in 
producingit, the ridges and inequalities of the trace 
can be made to agitate a light stylus resting on 
them, and cause it to set the delicate tympan into 
vibrations corresponding very accurately to those 
of the original sounds. The tympan employed 
for receiving is made of gold-beater's skin, having 
a stud at its centre and a sprmgy stylus of steel 
wire. The sounds emitted by this device are 
almost a whisper as compared to the original ones, 
but they are faithful in articulation, which is the 
main object, and they are conveyed to the ear by 
means of flexible hearing-tubes. 

These tympans are interchangeable at will, 



i6o 



THE STORY OF ELECTRICITY. 



and the arm which carries them is also provided 
with a turning tool for smoothing the wax cylin- 
der prior to its receiving the print. The cylinders 
are made of different sizes, from i to 8 inches 
long and 4 inches in diameter. The former has a 
storage capacity of 200 words. The next in size 
has twice that, or 400 words, and so on. Mr. 
Edison states that four of the large 8-inch cylin- 
ders can record all '^ Nicholas Nickleby," which 
could therefore be automatically read to a private 
invalid or to a number of patients in a hospi- 
tal simultaneously, by 
means of a bunch of 
hearing- tubes. The 
cylinders can be read- 
ily posted like letters, 
and made to deliver 
their contents viva voce in a du- 
plicate phonograph, every tone 
and expression of the writer be- 
ing rendered with more or less 
fidelity. The phonograph has 
proved serviceable in recording 
the languages and dialects of van- 
ishing races, as well as in teaching 
pronunciation. 

The dimensions, form, and con- 
sequent appearance of the present 
commercial American phonograph 
are quite different from that above 
described, but the underlying principles and op- 
erations are identical. 

A device for lighting gas by the electric spark 
is shown in figure 95, where ^ is a flat vulcanite 
box, containing the apparatus which generates 
the electricity, and a Stem or pointer B^ which 




Fig. 95. — An 
Electric Gas 
Lighter. 



MINOR USES OF ELECTRICITY. i6l 

applies the spark to the gas jet. The generator 
consists of a small 'Mntluence " machine, which is 
started by pressing the thumb-key C on the side 
of the box. The rotation of a disc inside the box 
produces a supply of static electricity, which 
passes in a stream of sparks between two contact- 
points in the open end of the stem D. The latter 
is tubular, and contains a wire insulated from the 
metal of the tube, and forming with the tube the 
circuit for the electric discharge. The handle 
enables the contrivance to be readily applied. 
The apparatus is one of the few successful prac- 
tical applications of static electricity. 

Other electric gas-lighters consist of metal 
points placed on the burner, so that the electric 
spark from a small induction coil or dynamo 
kindles the jet. 

A platinum wire made white-hot by the pas- 
sage of a current is sometimes used to light 
lamps, as shown in figure 96, where JV is a small 
spiral of platinum connected in circuit with a 
generator by the terminals T T. When the lamp 
L is pressed against the button B the wire glows 
and lights it. 

Explosives, such as gunpowder and guncotton, 
are also ignited by the electric spark from an in- 
duction coil or the incandescence of a wire. Fig- 
ure 97 shows the interior of an ordinary electric 
fuse for blasting or exploding underground mines. 
It consists of a box of wood or metal primed 
with gunpowder or other explosive, and a plat- 
inum wire P soldered to a pair of stout copper 
wires /F, insulated with guttapercha. When the 
current is sent along these wires, the platinum 
glows and ignites the explosive. Detonating 
fuses are primed with fulminate of mercury. 
II 



I 



l62 



THE STORY OF ELECTRICITY. 



Springs for watches and other purposes are 
tempered by heating them with the current and 
quenching them in a bath of oil. 




Fig. 96. — An Electric Lamp Lighter. 



Electrical cautery is performed with an in- 
candescent platinum wire in lieu of the knife, 
especially for such operations as the removal of 
the tongue or a tumour. 

It was known to the ancients that a fish called 
a torpedo existed in the Mediterranean which 
was capable of administering a shock to persons 
and benumbing them. The torpedo, or " electric 
ray,'* is found in the Atlantic as well as the Med- 
iterranean, and is allied to the skate. It has an 
electric organ composed of 800 or 1000 polygonal 



MINOR USES OF ELECTRICITY. 



l6l 



cells in its head, and the discharge, which ap- 
pears to be a vibratory current, passes from the 




mTm 



Fig. 97. — An Electric Fuse. 



back or positive pole to the belly or negative pole 
through the water. T\\t gyniotus^ or Surinam eel, 
which attains a length of five or six feet, has an 
electric organ from head to tail, and can give a 
shock sufficient to kill a man. Humboldt has 
left a vivid picture of the frantic struggles of wild 
horses driven by the Indians of Venezuela into the 
ponds of the savannahs infested by these eels, in 
order to make them discharge their thunderbolts 
and be readily caught. 

Other fishes — the siliinis^ vialapteninis^ and so 
on — are likewise endowed with electric batteries 
for stunning and capturing their prey. The ac- 
tion of the organs is still a mystery, as, indeed, is 
the w^hole subject of animal electricity. Nobili 
and Matteucci discovered that feeble currents 
are generated by the excitation of the nerves and 
the contraction of the muscles in the human sub- 
ject. 

Electricity promises to become a valuable 
remedy, and currents — continuous, intermittent, 
or alternating — are applied to the body in nerv- 
ous and muscular affections with good effect; 
but this should only be done under medical ad- 
vice, and with proper apparatus. 

In many cases of severe electric shock or 
lightning stroke, death is merely apparent, and 



164 



THE STORY OF ELECTRICITY. 



the person may be brought back to life by the 
method of artificial respiration and rhythmic trac- 
tion of the tongue, as applied to the victims of 
drowning or dead faint. 

A good lightning conductor should not have 
a higher electrical resistance than 10 ohms from 
the point to the ground, including the " earth '* 
contact. Exceptionally good conductors have 
only about 5 ohms. A high resistance in the rod 
is due either to a flaw in the conductor or a bad 
earth connection, and in such a case the rod may 
be a source of danger instead of security, since 
the discharge is apt to find its way through some 
part of the building to the ground, rather than 
entirely by the rod. It is, therefore, important to 
test lightning conductors from time to time, and 
the magneto-electric tester of Siemens, which we 
illustrate in figures 98 and 99, is very serviceable 




Fig. 98. 



for the purpose, and requires no battery. The 
apparatus consists of a magneto-electric machine 
J/", which generates the testing current by turn- 
ing a handle, and a Wheatstone bridge. The 



MINOR USES OF ELECTRFCITV. 



165 



latter comprises a ring of German silver wire, 
forming two branches. A contact lever P moves 
over the ring, and is used as a battery key. A 
small galvanometer G shows the indications of 




Fig. 99. 



the testing current. A brass sliding piece ^ puts 
the galvanometer needle in and out of action. 
There are also several connecting terminals, b b\ 
/, c^c, and a comparison resistance R (figure 98). 
A small key K is fixed to the terminal / (figure 
99), and used to put the current on the lightning- 
rod, or take it off at w^ill. A leather bag A at 
one side of the wooden case (figure 99) holds a 
double conductor leading wire, which is used for 
connecting the magneto-electric machine to the 
bridge. On turning the handle of M the current 
is generated, and on closing the key K it circu- 
lates from the terminals of the machine through 
the bridge and the lightning-rod joined with the 
latter. The needle of the galvanometer is de- 
flected by it, until the resistance in the box R is 
adjusted to balance that in the rod. When this 



1 66 THE STORY OF ELECTRICITY. 

is SO, the galvanometer needle remains at rest. 
In this way the resistance of the rod is told, and 
any change in it noted. In order to effect the 
test, it is necessary to have two earth plates, E^ 
and ^^, one (^^) that of the rod, and the ot^er 
(iS"^) that for connecting to the testing apparatus 
by the terminal b^ (figure 99). The whole instru- 
ment only weighs about 9 lbs. In order to test 
the " earth '* alone, a copper wire should be sol- 
dered to the rod at a convenient height above the 
ground, and terminal screws fitted to it, as shown 
at T (figure 99), so that instead of joining the 
whole rod in circuit with the apparatus, only that 
part from 7" downwards is connected. The Hon. 
R. Abercrombie has recently drawn attention to 
the fact that there are three types of thunder- 
storm in Great Britain. The first, or squall 
thunderstorms, are squalls associated with thun- 
der and lightning. They form on the sides of 
primary cyclones. The second, or commonest 
thunderstorms, are associated with secondary cy- 
clones, and are rarely accompanied by squalls. 
The third, or line thunderstorms, take the form 
of narrow bands of rain and thunder — for ex- 
ample, 100 miles long by 5 to 10 miles broad. 
They cross the country rapidly, and nearly broad- 
side on. These are usually preceded by a violent 
squall, like that which capsized the Eurydice, 

The gloom of January, 1896, with its war and 
rumours of war, was, at all events, relieved by a 
single bright spot. Electricity has surprised the 
world with a new marvel, which confirms her 
title to be regarded as the most miraculous of all 
the sciences. Within the past twenty years she 
has given us the telephone of Bell, enabling Lon- 
don to speak with Paris, and Chicago with New 



MINOR USES OF ELECTRICITY. 167 

York ; the microphone of Hughes, which makes 
the tread of a fly sound Hke the '* tramp of an 
elephant," as Lord Kelvin has said ; the phono- 
graph of Edison, in which we can hear again the 
voices of the dead ; the electric light which glows 
without air and underwater, electric heat without 
fire, electric power without fuel, and a great deal 
more beside. To these triumphs we must now 
add a means of photographing unseen objects, 
such as the bony skeletons in the living body, 
and so revealing the invisible. 

Whether it be that the press and general pub- 
lic are growing more enlightened in matters of 
science, or that Professor Rontgen's discovery 
appeals in a peculiar way to the popular imagina- 
tion, it has certainly evoked a livelier and more 
sudden interest than either the telephone, micro- 
phone, or phonograph. I was present when Lord 
Kelvin first announced the invention of the tele- 
phone to a British audience, and showed the in- 
strument itself, but the intelligence was received 
so apathetically that I suspect its importance was 
hardly realised. It fell to my own lot, a few 
years afterwards, to publish the first account of 
the phonograph in this country, and I remember 
that, between incredulity on the one hand, and 
perhaps lack of scientific interest on the other, a 
considerable time elapsed before the public at 
large were really impressed by the invention. 
Perhaps the uncanny and mysterious results of 
Rontgen's discovery, which seem to link it with 
the " black arts," have something to do with 
the quickness of its reception by all manner of 
people. 

Like most, if not all, discoveries and inven- 
tions, it is the outcome of work already done by 



l68 THE STORY OF ELECTRICITY. 

Other men. In the early days of electricity it 
was found that when an electric spark from a 
frictional machine was sent through a glass bulb 
from which the air had been sucked by an air 
pump, a cloudy light filled the bulb, which was 
therefore called an '' electric egg.'' Hittorf and 
others improved on this effect by employing the 
spark from an induction coil and large tubes, 
highly exhausted of air, or containing a rare in- 
fusion of other gases, such as hydrogen. By this 
means beautiful glows of various colours, resem- 
bling the tender hues of the tropical sky, or the 
fleeting tints of the aurora borealis, were pro- 
duced, and have become familiar to us in the 
well-known Geissler tubes. 

Crookes, the celebrated English chemist, went 
still further, and by exhausting the bulbs with 
an improved Sprengel air-pump, obtained an 
extremely high vacuum, which gave remarkable 
effects (page 120). The diffused glow or cloudy 
light of the tube now shrank into a single stream, 
which joined the sparking points inserted through 
the ends of the tube as with a luminous thread. 
A magnet held near the tube bent the streamer 
from its course; and there was a dark space or 
gap in it near the negative point or cathode, from 
which proceeded invisible rays, having the prop- 
erty of impressing a photographic plate, and of 
rendering matter in general on which they im- 
pinged phosphorescent, and, in course of time, 
red-hot. Where they strike on the glass of the 
tube it is seen to glow with a green or bluish 
phosphorescence, and it will ultimately soften 
with heat. 

These are the famous " cathode rays '* of which 
we have recently heard so much. Apparently 



MINOR USES OF ELECTRICITY. 169 

they cannot be produced except in a very high 
vacuum, where the pressure of the air is about 
i-iooth milHonth of an atmosphere, or that which 
it is some 90 or 100 miles above the earth. Mr. 
Crookes regards them as a stream of airy particles 
electrified by contact with the cathode or nega- 
tive discharging point, and repelled from it in 
straight lines. The rarity of the air in the tube 
enables these particles to keep their line without 
being jostled by the other particles of air in 
the tube. A molecular bombardment from the 
cathode is, in his opinion, going on, and when 
the shots, that is to say, the molecules of air, 
strike the wall of the tube, or any other body 
within the tube, the shock gives rise to phos- 
phorescence or fluorescence and to heat. This, 
in brief, is the celebrated hypothesis of '^ radiant 
matter," which has been supported in the United 
Kingdom by champions such as Lord Kelvin, Sir 
Gabriel Stokes, and Professor Fitzgerald, but 
questioned abroad by Goldstein, Jaumann, Wiede- 
mann, Ebert, and others. 

Lenard, a young Hungarian, pupil of the illus- 
trious Heinrich Hertz, was the first to inflict a 
serious blow on the hypothesis, by showing that 
the cathode rays could exist outside the tube in 
air at ordinary pressure. Hertz had found that a 
thin foil of aluminium was penetrated by the rays, 
and Lenard made a tube having a " window " of 
aluminium, through which the rays darted into 
the open air. Their path could be traced by the 
bluish phosphorescence which they excited in the 
air, and he succeeded in getting them to pene- 
trate a thin metal box and take a photograph in- 
side it. But if the rays are a stream of radiant 
matter which can only exist in a high vacuum, 



lyo THE STORY OF ELECTRICITY. 

how can they survive in air at ordinary pressure ? 
Lenard's experiments certainly favour the hy- 
pothesis of their being waves in the luminiferous 
ether. 

Professor Rontgen, of Wlirzburg, profiting by 
Lenard's results, accidentally discovered that the 
rays coming from a Crookes tube, through the 
glass itself, could photograph the bones in the 
living hand, coins inside a purse, and other ob- 
jects covered up or hid in the dark. Some bodies, 
such as flesh, paper, wood, ebonite, or vulcanised 
fibre, thin sheets of metal, and so on, are more or 
less transparent, and others, such as bones, car- 
bon, quartz, thick plates of metal, are more or 
less opaque to the rays. The human hand, for 
example, consisting of flesh and bones, allows 
the rays to pass easily through the flesh, but not 
through the bones. Consequently, when it is in- 
terposed between the rays and a photographic 
plate, the skeleton inside is photographed on the 
plate. A lead pencil photographed in this way 
shows only the black lead, and a razor with a 
horn handle only the blade. 

Thanks to the courtesy of Mr. A. A. Camp- 
bell Swinton, of the firm of Swinton & Stanton, 
the well-known electrical engineers, of Victoria 
Street, Westminster, a skilful experimentalist, 
who was the first to turn to the subject in Eng- 
land, I have witnessed the taking of these 
*^ shadow photographs," as they are called, some- 
what erroneously, for *^ radiographs '* or " crypto- 
graphs " would be a better word, and shall briefly 
describe his method. Rontgen employs an induc- 
tion coil insulated in oil to excite the Crookes 
tube and yield the rays, but Mr. Swinton uses a 
** high frequency current," obtained from appara- 



MINOR USES OF ELECTRICITY. 



171 







6 LcyocN 



n 






A 


1 




1 




ill 


iiii 










Fig. roo. — Photographing the Unseen. 



1)2 



THE STORY OF ELECTRICITY. 



tus similar to that of Tesla, and shown in figure 
loo, namely, a high frequency induction coil in- 
sulated by means of oil and excited by the con- 
tinuous discharge of twelve half-gallon Leyden 
jars charged by an alternating current at a pres- 
sure of 20,000 volts produced by an ordinary 
large induction coil sparking across its high pres- 
sure terminals. 

A vacuum bulb connected between the dis- 
charge terminals of the high frequency coil, as 




Fig. ioi. — Photo^aphing the Skeleton, 

shown in figure loi, was illuminated with a pink 
glow, which streamed from the negative to the 
positive pole — that is to say, the cathode to the 
anode, and the glass became luminous with bluish 
phosphorescence and greenish fluorescence. Im- 
mediately under the bulb was placed my naked 
hand resting on a photographic slide containing 
a sensitive bromide plate covered with a plate 
of vulcanised fibre. An exposure of five or ten 
minutes is sufficient to give a good picture of the 
bones, as will be seen from the frontispiece. 



MINOR USES OF ELECTRICITY. 



173 



The term " shadow " photograph requires a 
word of explanation. The bones do not appear 
as flat shadows, but rounded like solid bodies, as 
though the active rays passed through their sub- 
stance. According to Rontgen, these '' x " rays, 
as he calls them, are not true cathode rays, partly 
because they are not deflected by a magnet, but 
cathode rays transformed by the glass of the 
tube ; and they are probably not ultra-violet 
rays, because they are not refracted by water or 
reflected from surfaces. He thinks they are the 
missing *^ longitudinal " rays of light whose ex- 
istence has been conjectured by Lord Kelvin and 
others — that is to say, waves in which the ether 
sways to and fro along the direction of the ray, 
as in the case of sound vibrations, and not from 
side to side across it as in ordinary light. 

Be this as it may, his discovery has opened 
up a new field of research and invention. It has 
been found that the immediate source of the rays 
is the fluorescence and phosphorescence of the 
glass, and they are more effective when the fluor- 
escence is greenish-yellow or canary colour. Cer- 
tain salts — for example, the sulphates of zinc and 
of calcium, barium platino-cyanide, tungstate of 
calcium, and the double sulphate of uranyle and 
potassium — are more active than glass, and even 
emit the rays after exposure to ordinary light, if 
not also in the dark. Salvioni of Perugia has 
invented a '' cryptoscope," w^hich enables us to 
see the hidden object without the aid of photog- 
raphy by allowing the rays to fall on a plate 
coated wMth one of these phosphorescent sub- 
stances. Already the new method has been 
applied by doctors in examining malformations 
and diseases of the bones or internal organs, and 



174 THE STORY OF ELECTRICITY. 

in localising and extracting bullets, needles, or 
other foreign matters in the body. There is little 
doubt that it will be very useful as an adjunct to 
hospitals, especially in warfare, and, if the appa- 
ratus can be reduced in size, it will be employed 
by ordinary practitioners. It has also been used 
to photograph the skeleton of a mummy, and to 
detect true from artificial gems. However, one 
cannot now easily predict its future value, and 
applications will be found out one after another 
as time goes on. 



CHAPTER X. 

THE WIRELESS TELEGRAPH. 

Magnetic waves generated in the ether (see 
pp. 53-95) by an electric current flowing in a 
conductor are not the only waves which can be 
set up in it by aid of electricity. A merely station- 
ary or ** static " charge of electricity on a body, 
say a brass ball, can also disturb the ether ; and if 
the strength of the charge is varied, ether oscilla- 
tions or waves are excited. A simple way of pro- 
ducing these ^'electric waves" in the ether is to 
vary the strength of charge by drawing sparks 
from the charged body. Of course this can be 
done according to the Morse code; and as the 
waves after travelling through the ether with the 
speed of light are capable of influencing conduc- 
tors at a distance, it is easy to see that signals 
can be sent in this way. The first to do so in a 
practical manner was Signer Marconi, a young 
Italian hitherto unknown to fame. In carrying 



THE WIRELESS TELEGRAPH. i ; :^ 

out his invention, Marconi made use of facts well 
known to theoretical electricians, one of whom, 
Dr. Oliver J. Lodge, had even sent signals with 
them in 1894; but it often happens in science as 
in literature that the recognised professors, the 
men who seem to have everything in their favour 
— knowledge, even talent — the men whom most 
people would expect to give us an original dis- 
covery or invention, are beaten by an outsider 
whom nobody heard of, who had neither learn- 
ing, leisure, nor apparatus, but what he could pick 
up for himself. 

Marconi produces his waves in the ether by 
electric sparks passing between four brass balls, 
a device of Professor Righi, following the classical 
experiments of Heinrich Hertz. The balls are 
electrified by connecting them to the well-known 
instrument called an induction coil, sometimes 
used by physicians to administer gentle shocks to 
invalids ; and as the working of the coil is started 
and stopped by an ordinary telegraph key for in- 
terrupting the electric current, the sparking can 
be controlled according to the Morse code. In 
our diagram, which explains the apparatus, the 
four balls are seen at D, the inner and larger pair 
bemg partly immersed in vaseline oil, the outer 
and smaller pair being connected to the secondary 
or induced circuit of the induction coil C, which 
is represented by a wavy line. The primary or 
inducing circuit of the coil is connected to a 
battery B through a telegraph signalling key K, 
so that when this key is opened and closed by 
the telegraphist according to the Morse code, the 
induction coil is excited for a longer or shorter 
time by the current from the battery, in agree- 
ment with the longer and shorter signals of the 



176 THE STORY OF ELECTRICITY. 

message. At the same time longer or shorter 
series of sparks corresponding to these signals 
pass across the gaps between the four balls, and 
give rise to longer or shorter series of etheric 
waves represented by the dotted line. So much 
for the *^ Transmitter." But how does Marconi 
transform these invisible waves into visible or 
audible signals at the distant place ? • He does 
this by virtue of a property discovered by Mr. S. 
A. Varley as far back as 1866, and investigated by 
Mr. E. Branly in 1889. They found that powder 
of metals, carbon, and other conductors, while 
offering a great resistance to the passage of an 
electric current when in a loose state, coheres to- 
gether when electric waves act upon it, and op- 
poses much less resistance to the electric current. 
It follows that if a Morse telegraph instrument at 
the distant place be connected in circuit with a 
battery and some loose metal dust, it can be 
adjusted to work when the etheric waves pass 
through the dust, and only then. In the diagram 
R is this Morse *' Receiver " joined in circuit with 
a battery B^ ; and a thin layer of nickel and silver 
dust, mixed with a trace of mercury, is placed be- 
tween two cylindrical knobs or *^ electrodes" of 
silver fused into the glass tube d, which is ex- 
hausted of air like an electric glow lamp. Now, 
when the etheric waves proceeding from the trans- 
mitting station traverse the glass of the tube and 
act upon the metal dust, the current of the battery 
B^ works the Morse receiver, and marks the sig- 
nals in ink on a strip of travelling paper. Inas- 
much as the dust tends to stick together after a 
wave passes through it, however, it requires to be 
shaken loose after each signal, and this is done by 
a small round hammer head seen on the right, 



THE WIRELESS TELEGRAPH. 



177 



which gives a sHght tap to the tube. The ham- 
mer is worked by a small electromagnet E, con- 
nected to the Morse instrument, and another 
battery b in what is called a *' relay " circuit; 








TRAN^MTTTWa STATION RECEIVING STATION 

Fig. 102. — Marconi's Apparatus. 

so that after the IMorse instrument marks a sig- 
nal, the hammer makes a tap on the tube. As 
this tap has a bell-like sound, the telegraphist can 
also read the signals of the message by his ear. 

Two '* self-induction bobbins," L L\ a well- 
known device of electricians for opposing resist- 
ance to electric waves, are included in the circuit 
of the Morse instrument the better to confine the 
action of the waves to the powder in the tube. 
Further, the tube d is connected to two metal 
conductors V V^, which may be compared to reso- 
nators in music. They can be adjusted or attuned 
to the electric waves as a string or pipe is to 
sonorous waves. In this way the receiver can be 
made to work only when electric waves of a cer- 
tain rate are passing through the tube, just as a 
tuning-fork resounds to a certain note ; it being 
12 



178 THE STORY OF ELECTRICITY. 

understood that the length of the waves can 
be regulated by adjusting the balls of the trans- 
mitter. As the etheric waves produced by the 
sparks, like ripples of water caused by dropping 
a stone into a pool, travel in all directions from 
the balls, a single transmitter can work a number 
of receivers at different stations, provided these 
are *' tuned *' by adjusting the conductors V V^ to 
the length of the waves. It is, therefore, pos- 
sible to transmit secret messages by concealing 
the nature of the tuning adjustment, which is 
quite delicate. Marconi has succeeded in send- 
ing telegrams through the air in this way for from 
twelve to fifty miles. Changes of the weather, 
such as rain, fog, wind, and snow, do not affect 
the operation. It is possible, however, that thun- 
derstorms may sometimes disturb the action, be- 
cause lightning flashes may give rise to electric 
waves in the ether. In order to prevent inter- 
vening hills, houses, and other objects from stop- 
ping the signals, the apparatus can be raised on 
masts, or connected with exposed conductors, so 
as to clear the obstacle. 

It is obvious that the new wireless telegraph 
will be useful in communicating between ship and 
ship at sea or ship and shore, or lighthouse and 
coastguard. It is likely to prove serviceable as a 
fog-signal and prevent collisions at sea, if not on 
land. It will enable trains, balloons, and other 
vehicles to send messages as they go. Moreover, 
it will permit soldiers in the field to keep in touch 
with each other, and outlying folk on islands and 
mountains with the rest of the world. 



LIST OF ROOKS. 



Thomson's Elementary Lessons in Electricity and Magnetism. 
Macmillan. 

Thomson's Translation of Guillemin's Electricity a?iil Mag- 
netism. Macmillan. 

Foster and Atkinson's Adaptation of Joubert's Elementary 
J realise on Electricity and Magnetism. Longmans. 

Mendenhall's Century of Electricity. Macmillan. 

Jamieson's Elementary Manual of Electricity and Magnetism^ 
Griffin. 

Burch's Manual of Electric Science. Methuen. 

Bottone's Electricity and Magttetism. Whittaker. 

Stewart's Text-book of Magnetism and Electricity, Clive. 

Pope and Brackett's Electricity in Daily Life. Kegan Paul. 

Trevert's Electricity and its Recent Applications. Alabaster & 
Gatehouse. 

Trevert's Everybody's LLandbook of Electricity. Alabaster & 
Gatehouse. 

Electrical Apparatus for Amateurs. Ward & Lock. 

Gillett's Phonograph, and I/ow to Construct it. Spon. 

Ayrton's Practical Electricity. Cassells. 

Fleming's Short Lectures to Electrical A rtisatis, Spon. 

Slingo and Brooker's Electrical Engineering. Longmans 

Preece and Sievewright's Telegraphy. Longmans. 

Preece and Stubbs' Manual of 7\'/ephony. Whittaker. 

Poole's Practical Telephone Handbook. W^hittaker. 

Bottone's Dynamo : ILo7u Made and How Used. Sonnen- 
schein. 

Bottone's Electro-motors : LIoiv Made and LIoio Used. Whit- 
taker. 

Wallis and Hawkin's Dynamos. Whittaker. 

All sop's Induction Coils. Spon. 

Allsop's Practical Electric Lighting. Whittaker. 

Bax's Popular Electric Lighting. Biggs. 

179 



l8o LIST OF BOOKS. 

Bottone's Guide to Electric Lighting for Householder 5» Whit- 
taker. 

Gordon's Decorative Electricity. Low. 

Reckenzaum's Electric Traction, Biggs. 

Gore's Electro-C hemistry. Electrician Co. 

Benjamin's Voltaic Cell. Wiley, of New York. 

Niblett's Secondary Batteries. Biggs. 

Sloane's Standard Electrical Dictionary. Lockwood. 

Maycock's Practical Electrical Notes and Definitions. Spon. 

Trevert's Electrical Measurements for Amateurs. Alabaster 
& Gatehouse. 

Southam's Electrical Engineering as a Profession. Whit- 
taker. 

Field's Story of the Atlantic Cable. Gay & Bird. 



APPENDIX. 



UNITS OF MEASUREMENT. 

[Fro?n Munro and Jamiesons Pocket-book of Elec- 
trical Rules and Tables). 

I. Fundamental Units. — The electrical 
units are derived from the following mechanical 
units : — 

The Centifnetre as a unit of le?igth ; 
The Gramme as a unit of mass ; 
The Second as a unit of time. 
The Centi??ietre is equal to 0.3937 ^^^h in 
length, and nominally represents one thousand- 
millionth part, or yinro^oTro.Tnro" ^^ ^ quadrant of 
the earth. 

The Gramme is equal to 15.432 grains, and 
represents the mass of a cubic centimetre of wa- 
ter at 4° C. Mass is the quantity of matter in 
a body. 

The Second \s the time of one swing of a pen- 
dulum making 86,164.09 swings m a sidereal day, 
or 7rg-,4 on P^^t ^^ ^ mean solar day. 

II. Derived Mechanical Units. — 

Area. — The unit of area is the square centi- 
metre. 

i8i 



1 82 APPENDIX. 

Volume, — The unit of volume is the cubic centt- 
metre. 

Velocity is rate of change of position. It in- 
volves the idea of direction as well as that of 
magnitude. Velocity is uniform when equal spaces 
are traversed in equal intervals of time. The 
unit of velocity is the velocity of a body which 
moves through unit distance in unit time, or the 
velocity of one centimetre per second. 

Momentum is the quantity of motion in a body, 
and is measured by mass x velocity. 

Acceleration is the rate of change of velocity, 
whether that change take place in the direction 
of motion or not. The unit of acceleration is 
the acceleration of a body which undergoes unit 
change of velocity in unit time, or an acceleration 
of one centimetre-per-second per second. The 
acceleration due to gravity is considerably greater 
than this, for the velocity imparted by gravity to 
falling bodies in one second is about 981 centi- 
metres per second (or about 32.2 feet per second). 
The value differs slightly in different latitudes. 
At Greenwich the value of the acceleration due to 
gravity is ^ = 981.17 ; at the Equator g = 978.1 ; 
at the North Pole g — 983.1. 

Force is that which tends to alter a body's 
natural state of rest or of uniform motion in a 
straight line. 

Force is measured by the acceleration which 
it imparts to mass — i. e., mass X accelera- 
tion. 

The Unit of Force, or Dyne, is that force which, 
acting for one second on a mass of one gramme, 
gives to it a velocity of one centimetre per 
second. The force with which the earth attracts 
any mass is usually called the ** weight " of that 



APPENDIX. 183 

mass, and its value obviously differs at different 
points of the earth's surface. The force with 
which a body gravitates — i.e., its weight (in 
dynes), is found by multiplying its mass (in 
grammes) by the value of ^i,^ at the particular 
place where the force is exerted. 

Work is the product of a force and a distance 
through which it acts. The unit of work is the 
work done in overcoming unit force through 
unit distance — /. e., in pushing a body through a 
distance of one centimetre against a forch of one 
dyne. It is called the Erf^. Since the ** weight '* 
of one gramme is i X 981 or 981 dynes, the work 
of raising one gramme through the height of one 
centimetre against the force of gravity is 981 
ergs or^ergs. One kilogramme-metre = 100,000 
{g) ergs = 9.81 X 10^ ergs. One foot-pound = 
13*825 i^g) ergs, = 1.356 X 10^ ergs. 

Energy is that property which, possessed by a body, gives 
it the capability of doing work. Kinetic energy is the work a 
body can do in virtue of its motion. Potential energy is the 
work a body can do in virtue of its position. The unit of 
energy is the Erg. 

Power or Activity is the rate of w^ork; the prac- 
tical unit is called the Watt — 10'' ergs per second. 
A Horse-power = 33,000 ft. -lbs. per minute = 
550 ft. -lbs. per second ; but as seen above under 
Work, I ft. -lb. = 1-356 X 10' ergs, and under 
Power, I Watt =10' ergs per sec. .*. a Horse- 
poiuer = 550 X 1.356 X 10^ ergs = 746 Watts; 

EC C'R E" yj p 

746 746 746 R 
where E = volts, C = amperes, and R = ohms. 

The French ''force de c/ievar' = 75 kilogramme 
metres per sec. = 736 Watts — 542.48 ft. -lbs. per 



1 84 APPENDIX. 

sec. =: '9863 H.P. ; or one H.P. = i. 01385 ^' force 
de chevaiy 

Derived Electrical "Units. — There are two sys- 
tems of electrical units derived from the funda- 
mental ^^ C.G.S.*' units, one set being based upon 
the force exerted between two quantities of elec- 
tricity, and the other upon the force exerted be- 
tween two magnetic poles. The former set are 
termed electro-static units, the latter electro-magnetic 
units. 

III. Electrostatic Units. — 

Unit quantity of electricity is that which repels 
an equal and similar quantity at unit distance 
with unit force in air. 

Unit current is that which conveys unit quan- 
tity of electricity along a conductor in a second. 

Unit electromotive force, or U7iit difference of 
potential exists between two points when the unit 
quantity of electricity in passing from one to the 
other will do the unit amount of work. 

Unit resistance \s that of a conductor through 
which unit electromotive force between its ends 
can send a unit current. 

Unit capacity is that of a condenser which con- 
tains unit quantity when charged to unit differ- 
ence of potential. 

IV. Magnetic Units. — 

Unit magnetic pole is that which repels an equal 
and similar pole at unit distance with unit force 
in air. 

Strength of Magnetic Field at any point is 
measured by the force which would act on a unit 
magnetic pole placed at that point. 



APPENDIX. 185 

Unit Intensity of Field \s that intensity of field 
which acts on a unit pole with unit force. 

Moment 0/ a Mii!::^ net is the strength of either 
pole multiplied by the distance between the poles. 

Intensity of Magnetisation is the magnetic mo- 
ment of a magnet divided by its volume. 

Magnetic Potential. — The potential at a point 
due to a magnet is the work that must be done in 
removing a unit pole from that point to an in- 
finite distance against the magnetic attraction, or 
in bringing up a unit pole from an infinite dis- 
tance to that point against the magnetic repul- 
sion. 

Unit Differenee of Mag net ie Potential. — Unit 
difference of magnetic potential exists between 
two points when it requires the expenditure of 
one erg of work to bring an (N. or S.) unit mag- 
netic pole from one point to the other against the 
magnetic forces. 

V. Electro-Magnetic Units. — 

Unit current is that which in a wire of unit 
length, bent so as to form an arc of a circle of 
unit radius, would act upon a unit pole at the 
centre of the circle with unit force. 

Unit quantity of electricity is that which a unit 
current conveys in unit time. 

Unit electro-motive force or difference of potential 
is that which is produced in a conductor moving 
through a magnetic field at such a rate as to cut 
one unit line per second. 

Unit resistance is that of a conductor in which 
unit current is produced by unit electro-motive 
force between its ends. 

Unit capacity is that of a condenser which will 



1 86 APPENDIX. 

be at unit difference of potential when charged 
with unit quantity. 

Electric and magnetic force varies inversely as the square 
of the distance. 

PRACTICAL UNITS OF ELECTRICITY. 

Resistance — R. — The Ohm is the resistance 
of a column of mercury 106.3 centimetres long, 
I square millimetre in cross-section, weighing 
14.4521 grammes, and at a temperature of 0° 
centigrade. Standards of wire are used for prac- 
tical purposes. The ohm is equal to a thou- 
sand million, 10^, electromagnetic or Centimetre- 
Gramme-Second (" C. G. S.") units of resistance. 
The megohm is one million ohms. 
The microhm is one millionth of an ohm. 
Electromotive Force — E. — The Volt is that 
electromotive force which maintains a current of 
one ampere in a conductor having a resistance of 
one ohm. The electromotive force of a Clark 
standard cell at a temperature of 15° centigrade 
is 1.434 volts. The volt is equal to a hundred 
million, 10^, C. G. S. units of electromotive force. 
Current — C. — The Ampere is that current which 
will decompose 0.09324 milligramme of water 
(HgO) per second or deposit 1.118 milli- 
grammes of silver per second. It is equal to 
one-tenth of a C. G. S. unit of current. 
The 7mlliampere is one thousandth of an ampere. 
Quantity — Q. — The Coulomb is the quantity of 
electricity conveyed by an ampere in a sec- 
ond. It is equal to one-tenth of a C. G. S. 
unit of quantity. 
The micrO'Coulofnb is one millionth of a coulomb. 
Capacity — K. — The Farad is that capacity of a 



APPENDIX. I §7 

body, say a Leyden jar or condenser, which 
a coulomb of electricity will charge to the 
potential of a volt. It is equal to one thou- 
sand-millionth of a C. G. S. unit of capacity. 

The micro-farad is one millionth of a Farad. 

By Oluns Laic, Current i= Electromotive Force -^- 
Resistance, 

orC = j^ 

Volt 

Ampere = y^, — 

^ Ohm 

Hence when we know any two of these quan- 
tities, we can find the third. For example, if 
we know the electromotive force or differ- 
ence of potential in volts and the resistance 
in ohms of an electric circuit, w^e can easily 
find the current in amperes. 
Power — P. — The JVatt is the power conveyed by 
a current of one ampere through a conductor 
whose ends differ in potential by one volt, or, 
in other words, the rate of doing work when 
an ampere passes through an ohm. It is 
equal to ten million, lo^, C. G. S. units of 
power or ergs per second, that is to say, to a 
Joule 

per second, or of a horse-powder. 

746 

A Watt = volt X ampere, and a Horse-power = 
Watts -T- 746. 

Heat or Work — W. — Tht Joule is the work done 
or heat generated by a Watt in a second, that 
is, the work done or heat generated in a sec- 
ond by an ampere flowing through the resist- 
ance of an ohm. It is equal to ten million, 
10^, C. G. S. units of work or ergs. Assum- 



1 88 APPENDIX. 

ing "Joule's equivalent" of heat and me- 
chanical energy to be 41,600,000, it is the 
heat required to raise .24 gramme of water 1° 
centigrade. A Joule = Volt X ampere X sec- 
ond. Since i horse-power = 550 foot pounds 
of work per second, 

W= SS^E.Q. = .7373 E.Q. foot pounds. 
746 

Heat Units. 

The British Unit is the amount of heat required 
to raise one pound of water from 60° to 61° 
Fahrenheit. It is 251.9 times greater than 
the metric unit, therm or calorie, which is the 
amount of heat required to raise one gramme 
of water from 4° to 5° centigrade. 

Joule s Equivale?it — J. — ^is the amount of energy 
equivalent to a therm or calorie, the metric 
unit of heat. It is equal to 41,600,000 ergs. 

The heat in therms generated in a wire by a 
current = Volt X ampere X time in seconds 
X 0.24. 

Light Units 

The British Unit is the light of a spermaceti 
candle '^l<^-mQ\\ in diameter, burning 120 grains 
per hour (six candles to the pound). They 
sometimes vary as much as 10 per cent, from 
the standard. Mr. Vernon Harcourt's stand- 
ard flame is equal to an average standard 
candle. 

The French Unit is the light of a Carcel lamp, 
and is equivalent to 9^/2 British units. 



INDEX. 



Amber, g. 
Ampere, 76, 186. 
Accumulator, 39. 

E. P. S., 40. 

Faure, 3Q. 

Grove gas, 39. 

Plante, 30. 

Sellon-Volckmar, 40. 
Appendix, 181. 
Arc, electric, no, 122. 

B. 

Books, list of, 179. 

C. 

Capacity, 186. 

Coal, electricity from, 131. 

Code, Morse telegraph, 87, loi. 

Compass, mariner's, 46. 

Condenser, 62. 

Conduction, 16. 

Conductors, 16. 

Coulomb, 76, 186. 

Current, electric, 57. 

electromotive force of, 74. 

attraction of, 57. 

Ohm's law for, 76. 

potential of, 75. 

pressure of, 74. 
Currents, electric, resistance of, 74, 



75- 
rules for direction of, 56, 65, 66. 

D. 

Diamagnetism, 51. 
Dynamos, 67. 

compound, 73. 

Gramme, 69. 



Dynamos, magneto-electric, 67. 
reversibility of, 65, 73. 
series, 70. 
shunt, 71. 



Electric alarms, 146. 

burglar, 148. 

fire, 147. 

frost, 149. 

torpedo, 149. 

water, 149. 
Electric arc, no. 

arc lamps, in. 

bell, 143. 

boat, 128. 

carriage, 128. 

chronograph, 151. 

circuits, 118. 

city, 132. 

clocks, 150. 

compass, 150. 

cooking, 123. 

cut-outs, 120. 

divining rod, 155. 

drill, 133. 

fishes, 163. 

forces, II. 

furnace, 122. 

fuse, 163. 

gaslighter, 160. 

heat, 122. 

incandescent lamps, 123. 

induction glows, 120. 

light signals, 152. 

lamp-lighter, 162. 

log, 149. 

meters, 152. 

motor, 73. 

pen, 156. 

power, 124. 

power, transmission of, 125. 



189 



I go 



INDEX. 



Electric quilt, 124. 

radiator, 124. 

railway, 126. 

search light, 153. 

sewing machine, 132. 

shock, treatment for, 163. 

silhouettes, 167. 

torpedo, 130. 

tramway, 126. 

tricycle, 128. 

ventilator, 130. 

weather vane, 150. 

welding, 122. 
Electricity, chemistry and, 26. 

coal and, 131. 

friction and, 9. 

heat and, 41. 

magnetism and, 45, 

Niagara and, 1^2. 

origin of the science, 10. 

peat and, 131. 

scale of bodies producing, 14. 

surface, 17. 
Electro-cautery, 162. 
Electro-chemical equivalent, 77. 
Electro-chemistry, 26. 
Electro-deposition of metals, 77. 
Electrolysis, 74. 
Electromagnetism, 59. 
Electromagnet, 60. 
Electromedicine, 163. 
Electromotive force, 29, 74. 
Electrophorus, 20. 
Electroplating, 78. 
Electrotyping, 80, 
Energy, 183. 



Farad, 186. 



Galvanism, discovery of, 26. 
Galvanometer, 56. 
Galvanoscope, 56. 
Geissler tubes, 63, 168. 

H. 

Heat, 41, 188, 

unit, 184. 
Hysteresis, magnetic, 53, 



I. 



Induction, 18. 
balance, 154. 



Induction coil, 61. 

magneto electric, 154. 

magneto, direction of current, 56, 
66.^ 
Inductive capacity, 20. 
Insulation, 16. 
Insulators, 16. 
Ion, 76. 



Joule, 187, 

Joule's equivalent, 188. 

L. 

Leyden jar, 21. 
Light, unit, 188. 
Lightning, nature of, 25. 

rods, 25. 

rod testing, 164. 

shock, treatment for, 163. 
Lodestone, 46. 

M. 

Magnet, horse-shoe, 54. 

natural, 47. 
Magnetic compass, origin of, 46. 
Magnetic lines of force, 54, 57. 
Magnetism, 45. 

connection with electricity, 55. 

earth's, 49. 

earth's, forces of, 50. 

earth's, theory of, 52. 
Magnetite, 46. 
Measurement, units of, 181. 
Microphone, Hughes', 104. 
Morse code, 87. 

telegraph, 88. 
Motor, electric, 73. 

N. 
Niagara, electricity from, 1320 

O. 

Ohm. 76, 186. 
Ohm s law, 76, 187, 

P. 

Paramagnetism, 51. 
Peat, electricity from, 131, 
Peltier effect, 45. 
Phonograph, 156. 
Photo-electric cell, 154, 



INDEX. 



191 



Photophone, 153. 
Power, 183. 

Pressure of a current, 74. 
Primar>- cells, 37. 

coils, 61. 

current, 61. 



Resistance, 30. 



R. 



S. 



Secondary cells, 37. 

coils, 61. 

currents, 61. 
Shocks, electric, 163. 
Sonometer, 155. 
Sounder, 90. 
Storage cell, 37. 
Submarine cable, 95 

Atlantic, 96. 

circuit, 98. 

mirror instrument, 99. 

signal alphabet, loi. 

siphon recorder, 100. 

si>eed of messages, 10 1. 

detector, 155. 

T. 

Telautograph, 93. 
Telegrams, errors in, 92. 
Telegraph, automatic sender, 92. 

chemical, 90. 

circuit, 84. 

C. M.'s, 24. 

Cooke and Wheatstone, 82. 

domestic, 150. 

duplex system, 92. 

Hughes, 91. 

Kelvin, 99. 

Morse, 88. 

origin of, 81. 

Ronald's, 24. 

Vail, 90. 

wireless, 174. 



Telephone, Bell, 102. 

cable, 107. 

Chicago to New York, 107. 

Edison, 103. 

exchange, 107. 

instrument of Blake, 107. 

switchboard, 108. 
Thermo-electricity, 41. 
Thermo-electric couple, 41. 

in series, 43. 

piles, 44. 

scale, 42. 



U. 



Units, 181. 



Volt, 76, 186. 
Voltaic cell, 27. 

action of, 28. 

bichromate, 28. 

Bunsen. 33. 

Chloride of silver, 35. 

Clark Standard, 36. 

Coupling, 31. 

Darnell, 32. 

Dry ^'E. C. C," 36. 

Hellesen, 37. 

Leclanche-Barbier, 37. 

Grove, 33. 

Grove gas, 37. 

Leclanche, 34. 

Schanschieff, 36. 

Skrivanoff, 36. 

Smee, 33. 
Voltaic electricity, discovery of, 27, 
Voltameter, 38. 

W. 

Water, decomposition of, 37. 
Watt, 187. 

Wheatstone bridge, 164. 
Wireless telegraph, 174. 
i Work, 183, 187. 



THE END. 



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